Enhancements for resource allocation in wlan systems

ABSTRACT

A station may receive a frame transmitted to a plurality of STAs. The frame may indicate a first frequency resource allocated for the STA and a second frequency resource allocated for another STA of the plurality of STAs. The STA may transmit a data frame using the first frequency resource and receive an acknowledgement frame that acknowledges receipt of the data frame. The STA may receive a MU RTS frame transmitted to the plurality of STAs and may subsequently transmit a CTS frame in response to receipt of the MU RTS frame. The RTS/CTS transmissions may occur prior to transmission of the data frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/596,365 filed on Oct. 8, 2019 which is a continuation of U.S.application Ser. No. 15/948,869 filed on Apr. 9, 2018 which is acontinuation of U.S. application Ser. No. 15/026,666 filed on Apr. 1,2016, which is a National Stage Entry of PCT/US2014/058633, filed Oct.1, 2014, which claims the benefit of U.S. Provisional Application Ser.No. 61/885,400 filed on Oct. 1, 2013 and U.S. Provisional ApplicationSer. No. 61/979,099 filed on Apr. 14, 2014, the contents of which arehereby incorporated by reference herein.

BACKGROUND

A wireless local area network (WLAN) in an infrastructure basic serviceset (BSS) mode may include an access point (AP) for the BSS and one ormore stations (STAs), i.e., wireless transmit/receive units (WTRUs),associated with the AP. The AP may have access to or interface with aDistribution System (DS) or another type of wired/wireless network thatmay carry traffic in and out of the BSS. Traffic to STAs originatingfrom outside the BSS may arrive through the AP and may be delivered tothe STAs. Traffic to destinations outside the BSS originating from STAsmay be transmitted to the AP to be delivered to the respectivedestinations. Traffic between STAs within the BSS may also betransmitted through the AP, where the source STA may transmit traffic tothe AP, and the AP may deliver the traffic to the destination STA. Suchtraffic between STAs within a BSS may be referred to as peer-to-peer(P2P) traffic. P2P traffic may also be transmitted directly between thesource and destination STAs with a direct link setup (DLS) using anInstitute of Electrical and Electronics Engineers (IEEE) 802.11e DLS oran IEEE 802.11z tunneled DLS (TDLS). A WLAN in independent BSS (IBSS)mode may not include an AP, and thus the STAs may communicate directlywith each other. This mode of communication may be referred to as an“ad-hoc” mode of communication.

In an IEEE 802.11 infrastructure operation mode, the AP may transmit abeacon on a fixed channel known as the primary channel. The primarychannel may be 20 MHz wide and may be the operating channel of the BSS.The primary channel may also be used by the STAs to establish aconnection with the AP.

The channel access mechanism in an IEEE 802.11 system may be CarrierSense Multiple Access with Collision Avoidance (CSMA/CA). In thisoperation mode, every STA, including the AP, may sense the primarychannel. If the channel is detected to be busy, the STA may back off.Therefore, only one STA may transmit at any given time in a given BSS.

SUMMARY

A method and apparatus for use in an IEEE 802.11 station (STA) forreceiving data from an IEEE 802.11 access point (AP) via a coordinatedorthogonal block resource allocation (COBRA) is described. The STA mayreceive a COBRA schedule from the AP and transmit an acknowledgement(ACK) to the AP in the COBRA TXOP. The STA may receive a first datapacket in the COBRA TxOP based on the COBRA schedule. The STA maydetermine whether the first data packet is received successfully and ona condition that the first data packet is not received successfully, theSTA may transmit a negative acknowledgement (NACK) to the AP in theCOBRA TxOP.

A station may receive a frame transmitted to a plurality of STAs. Theframe may indicate a first frequency resource allocated for the STA anda second frequency resource allocated for another STA of the pluralityof STAs. The STA may transmit a data frame using the first frequencyresource and receive an acknowledgement frame that acknowledges receiptof the data frame. The STA may receive a multi-user (MU) request to send(RTS) frame transmitted to the plurality of STAs and may subsequentlytransmit a clear to send (CTS) frame in response to receipt of the MURTS frame. The RTS/CTS transmissions may occur prior to transmission ofthe data frame.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a diagram of an example Type I COBRA transmission;

FIG. 3 is a diagram of an example COBRA parameter set element.

FIG. 4 is an example of Type II COBRA transmission;

FIG. 5 is a diagram of an example multi-user diversity and sub-channelselection procedure;

FIG. 6 is a diagram of an example multi-user diversity and sub-channelselection procedure for a downlink transmission;

FIG. 7 is a diagram of an example multi-user diversity and sub-channelselection procedure for an uplink transmission;

FIG. 8 is a diagram of an example downlink COBRA-capable transmitter;

FIG. 9 is a diagram of an example downlink COBRA-capable receiver;

FIG. 10 is a graphical representation of simulation results ofmulti-user sub-channel selection with simulation scenario 1 with onedata stream transmission in both channel B and channel D;

FIG. 11 is a graphical representation of an empirical cumulativedistribution function (CDF) of channel magnitude difference oversub-channels;

FIG. 12 is a graphical representation of simulation results ofmulti-user sub-channel selection with two data stream transmission overchannel B with simulation scenario 2;

FIG. 13 is a graphical representation of simulation results ofmulti-user sub-channel selection with two data stream transmission overchannel D with simulation scenario 2;

FIG. 14 is a diagram of an example DL COBRA TXOP;

FIG. 15 is a diagram of an example UL COBRA TXOP;

FIG. 16 is a diagram of an example transmission failure of COBRAschedule information in DL COBRA;

FIG. 17 is a diagram of an example transmission failure in one of thesub-channels in DL COBRA;

FIG. 18 is a diagram of an example transmission failure of COBRA pollinformation in UL COBRA;

FIG. 19 is a diagram of an example transmission failure of COBRAschedule information in UL COBRA;

FIG. 20 is a diagram of an example transmission failure in one of thesub channels in UL COBRA;

FIG. 21 is a diagram of an example NACK control frame;

FIG. 22 is a diagram of an example uplink data buffer status feedbackprocedure;

FIG. 23 is a diagram of an example COBRA capability/operation element;

FIG. 24 is a diagram of an example ad hoc grouping management frame;

FIG. 25 is a diagram of an example ad hoc grouping management andtransmission procedure;

FIG. 26 is a diagram of an example COBRA DL schedule frame;

FIG. 27 is a diagram of another example COBRA DL schedule frame;

FIG. 28 is a diagram of an example COBRA UL schedule frame;

FIG. 29 is a diagram of a first example of a unified COBRA UL/DLschedule frame;

FIG. 30 is a diagram of a second example of a unified COBRA UL/DLschedule frame;

FIG. 31 is a diagram of a first example COBRA poll frame;

FIG. 32 is a diagram of a second example COBRA poll frame;

FIG. 33 is a diagram of an example COBRA uplink request (ULR) frame;

FIG. 34 is a diagram of an example A-MPDU format used to piggyback anACK frame to another frame;

FIG. 35 is a diagram of a first example channel access scheme forstandalone UL COBRA using a fixed or specific band assignment for ULRframe transmission for each STA;

FIG. 36 is a diagram of a second example channel access scheme forstandalone UL COBRA with code division multiplex (CDM) ULR;

FIG. 37 is a diagram of a third example channel access scheme forstandalone UL COBRA with time division multiplex (TDM) ULR;

FIG. 38 is a diagram of a first example channel access scheme forstandalone DL COBRA using a fixed or specific band assignment fordownlink COBRA transmission of each STA without an ACK from the assignedSTA;

FIG. 39 is a diagram of a second example channel access scheme forstandalone DL COBRA using a fixed or specific channel/band assignmentfor downlink COBRA transmission of each STA with an ACK from theassigned STAs;

FIG. 40 is a diagram of a first example combined downlink/uplink COBRAchannel access scheme using a fixed or specific channel/band assignmentfor both uplink and downlink COBRA transmission; and

FIG. 41 is a diagram of a second example combined downlink/uplink COBRAchannel access scheme using a fixed or specific channel/band assignmentfor downlink COBRA transmission and a frequency-selective channel/bandassignment for uplink COBRA transmission.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 106, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 106 and/or the removable memory 132.The non-removable memory 106 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth© module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. The RAN 104 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 116. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 104, andthe core network 106 may be defined as reference points.

As shown in FIG. 1C, the RAN 104 may include base stations 140 a, 140 b,140 c, and an ASN gateway 142, though it will be appreciated that theRAN 104 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 140 a, 140 b,140 c may each be associated with a particular cell (not shown) in theRAN 104 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the base stations 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the base station 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 140 a, 140 b, 140 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 142 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 106, and the like.

The air interface 116 between the WTRUs 102 a, 102 b, 102 c and the RAN104 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 106.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 106 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 140 a, 140 b,140 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 140 a, 140 b,140 c and the ASN gateway 142 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 100 c.

As shown in FIG. 1C, the RAN 104 may be connected to the core network106. The communication link between the RAN 104 and the core network 106may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 106 may include a mobile IP home agent(MIP-HA) 144, an authentication, authorization, accounting (AAA) server146, and a gateway 148. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 144 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 146 may be responsible for userauthentication and for supporting user services. The gateway 148 mayfacilitate interworking with other networks. For example, the gateway148 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 148 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1C, it will be appreciated that the RAN 104may be connected to other ASNs and the core network 106 may be connectedto other core networks. The communication link between the RAN 104 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 104 and the other ASNs. The communication link betweenthe core network 106 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

Herein, the terminology “STA” includes but is not limited to a wirelesstransmit/receive unit (WTRU), a user equipment (UE), a mobile station, afixed or mobile subscriber unit, a pager, a cellular telephone, apersonal digital assistant (PDA), a computer, a mobile Internet device(MID) or any other type of user device capable of operating in awireless environment. The STAs referenced herein may be COBRA capableSTAs, unless otherwise indicated.

Herein, the terminology “AP” includes but is not limited to a basestation, a Node-B, a site controller, or any other type of interfacingdevice capable of operating in a wireless environment. The APsreferenced herein may be COBRA capable APs, unless otherwise indicated.

References to COBRA, in addition to those descriptions cited herein, mayrefer to any block based coordinated reference allocation method whichmay be backward compatible to the CSMA air interface procedures andprotocols.

For reference, IEEE 802.11n and IEEE 802.11ac may operate in frequenciesfrom 2 to 6 GHz. In 802.11n, high throughput (HT) STAs may use a 40 MHzwide channel for communication. This may be achieved by combining aprimary 20 MHz channel with another adjacent 20 MHz channel to form a 40MHz wide channel. In 802.11ac, very high throughput (VHT) STAs maysupport 20 MHz, 40 MHz, 80 MHz and 160 MHz wide channels. While 40 MHzand 80 MHz channels may be formed by combining contiguous 20 MHzchannels, similar to 802.11n, a 160 MHz channel may be formed either bycombining 8 contiguous 20 MHz channels or two non-contiguous 80 MHzchannels (i.e., “80+80” configuration). As an example, for the “80+80”configuration, the data, after channel encoding, may be passed through asegment parser that divides it into two streams. Inverse fast Fouriertransform (IFFT) and time domain processing may be performed on eachstream separately. The streams may then be mapped on to the two channelsand the data may be sent out. On the receiving end, this mechanism maybe reversed, and the combined data may be sent to the medium accesscontrol (MAC) layer.

In addition, the request-to-send (RTS)/clear-to-send (CTS) shortinter-frame space (SIFS) may be 16 μs and the guard interval (GI) may be0.8 μs. Transmissions from nodes within 100 meters may remain within theGI. Transmissions from nodes beyond 100 meters may have a delay longerthan 0.8 μs. For example, at 1 kilometer, the delay may be over 6 μs.

For reference, IEEE 802.11af, and IEEE 802.11ah devices may operate infrequencies that are less than 1 GHz. For 802.11af and 802.11ah, thechannel operating bandwidths may be reduced as compared to 802.11n, and802.11ac. 802.11af may support 5 MHz, 10 MHz and 20 MHz wide bands intelevision (TV) white space (TVWS), while IEEE 802.11ah may support 1MHz, 2 MHz, 4 MHz, 8 MHz and 16 MHz in non-TVWS. Some STAs in 802.11ahmay be considered sensors with limited capabilities and may only support1 and 2 MHz transmission modes.

In WLAN systems that utilize multiple channel widths, such as 802.11n,802.11ac, 802.11af, and 802.11ah, there may be a primary channel thatmay have a bandwidth equal to the largest common operating bandwidthsupported by all STAs in the BSS. The bandwidth of the primary channelmay be limited by the STA that supports the smallest bandwidth operatingmode. In the example of 802.11ah, the primary channel may be 1 or 2 MHzwide if there are one or more STAs that only support 1 and 2 MHz modeswhile the AP and other STAs in the BSS may support 4 MHz, 8 MHz and 16MHz operating modes. All carrier sensing and network allocation vector(NAV) setting may depend on the status of the primary channel. Forexample, if the primary channel is busy due to a STA, supporting only 1and 2 MHz operating modes, transmitting to the AP, then the entireavailable frequency bands may be considered busy even though a majorityof the available frequency bands stay idle and available. In 802.11ahand 802.11af, packets may be transmitted using a clock that is downclocked 4 or 10 times as compared to 802.11ac.

In the United States, the available frequency bands that may be used by802.11ah are from 902 MHz to 928 MHz. In Korea it is from 917.5 MHz to923.5 MHz. In Japan, it is from 916.5 MHz to 927.5 MHz. The totalbandwidth available for 802.11ah may be 6 MHz to 26 MHz, depending onthe country code.

To improve spectral efficiency, 802.11ac has introduced a concept fordownlink multi-user multiple input multiple output (MU-MIMO)transmission to multiple STAs in the same symbol's time frame, forexample, during a downlink OFDM symbol. The potential for the use ofdownlink MU-MIMO is also currently considered for IEEE 802.11ah. Sincedownlink MU-MIMO, as referred to in IEEE 802.11ac, uses the same symboltiming to multiple STAs, interference of the waveform transmissions tomultiple STAs may not be an issue. However, all STAs involved in aMU-MIMO transmission with the AP may use the same channel or band. Thismay limit the operating bandwidth to the smallest channel bandwidth thatis supported by the STAs included in the MU-MIMO transmission with theAP.

Coordinated orthogonal block-based resource allocation (COBRA) in WLANsystems was first proposed by InterDigital. The COBRA transmissionscheme was proposed as an alternate means of WLAN medium access. TheCOBRA scheme may use a generic subcarrier based multiple access scheme.Solutions for COBRA may include multicarrier modulation, filtering, andtime, frequency, space, and polarization domains as the basis for thetransmission and coding scheme. The COBRA scheme may be implementedusing orthogonal frequency-division multiple access (OFDMA)sub-channelization, single-carrier frequency-division multiple access(SC-FDMA) sub-channelization, and filter-bank multicarriersub-channelization. The following features may be needed to enable COBRAtransmission: methods for coverage range extension; methods of groupingusers; methods for channel access; preamble designs for low overhead;methods for beam forming and channel sounding; methods for frequency andtiming synchronization; and methods for link adaptation. In addition,methods for grouping users may also be needed.

General COBRA Transmission Rule

A general transmission rule of COBRA is not well defined in existingCOBRA systems. For example, in some densely deployed systems, such asinfrastructure networks, COBRA-capable and non-COBRA-capable STAs mayco-exist in the same BSS or overlapping BSS (OBSS). In such a scenario,the AP may want to arrange part of a beacon interval for COBRAtransmission and the rest of the beacon interval for non-COBRAtransmission. Therefore, a defined transmission rule of COBRA thatallows COBRA transmission to coexist with non-COBRA transmission, e.g.,a CSMA/CA based channel access scheme is desired.

FIG. 2 is a diagram of an example Type I COBRA transmission. Type ICOBRA transmission is a mechanism to schedule COBRA and non-COBRAtransmissions during the same beacon interval. The AP may arrange partof a beacon interval for COBRA transmission using a beacon frame. Thebeacon frame may be used to announce one or more periods dedicated forCOBRA transmission in a given beacon interval. A COBRA period may be aperiod within a beacon interval, which only allows COBRAtransmission(s). As shown in FIG. 2, the beacon frame 205 may announceCOBRA period 210 is dedicated for COBRA transmission. A COBRA parameterset element may be included in the beacon frame. The rest of the timeslot or beacon interval may be allocated to non-COBRA transmission. Asshown in FIG. 2, the remaining portion of the beacon interval isallocated to legacy period 230.

FIG. 3 is a diagram of an example COBRA parameter set element 300. TheCOBRA parameter set element 300 may include an element ID field 305, alength filed 310, a COBRA period duration field 315, a COBRA basicsub-channel size field 320, a COBRA group bitmap field 325, a COBRAuplink random access present field 330, a COBRA group management presentfield 335 and a periodic COBRA period field 340.

The element ID field 305 may identify the specific element.

The length field 310 may indicate the length of the element.

The COBRA period duration field 315 may indicate the maximum length ofthe COBRA period in the current beacon interval. The STA may use thisfield to set its NAV. This field may also be used to set up an IEEE802.11 time unit (TU).

The COBRA basic sub-channel size field 320 may be used to indicate theminimum COBRA sub-channel size used in the current beacon interval.

The COBRA group bitmap field 325 may be a bitmap associated with theCOBRA group ID. When the COBRA group ID contains N group members, thisfield may include N bits. Each bit may be associated with one COBRAgroup. The value of the bit may be used to indicate whether the groupwill be assigned a COBRA transmission (downlink, uplink or combineddownlink/uplink) in the coming COBRA period within the beacon interval.

The COBRA uplink random access present field 330 may be used to indicatewhether the following COBRA period contains an uplink COBRA randomaccess transmission. An uplink COBRA random assess transmission may beused for COBRA non-AP STAs having uplink traffic to request the AP toassign uplink transmission.

The COBRA group management present field 335 may be used to indicatewhether the upcoming COBRA period contains COBRA group managementinformation.

The periodic COBRA period field 340 may be used to indicate whether theCOBRA period appears periodically, and if so may be used to indicate howoften the COBRA period field may appear. For example, it may indicatethat the COBRA period may appear every two beacon intervals.

COBRA transmission may be initiated and controlled by the AP in eitherdownlink COBRA transmission or uplink COBRA transmission. The AP maymaintain a COBRA schedule list, which may include the STAs that the APmay intend to communicate with. The list may include STAs the AP haspending traffic to transmit to; the STAs which have traffic to transmitto the AP; or the STAs the AP intends to poll, and the like. Referringback to FIG. 2, the COBRA schedule list maintained by the AP may includeSTAs 1-6, with an indication that the AP has pending traffic to transmitto these STAs. If the COBRA schedule list is not empty, the AP mayallocate a COBRA period by including the COBRA parameter set element inthe beacon frame, as described above. The decision of when to allocate aCOBRA period may be implementation dependent. Alternatively oradditionally, the AP may transmit a COBRA schedule frame to one or moreSTAs to initiate communications between the AP and the STAs. The STAsmay then be aware of their transmission or reception position in theCOBRA period within the beacon interval. For the example provided inFIG. 2, the COBRA schedule frame (not shown) would indicate the AP has aCOBRA transmission for STA-1 and STA-2 and another COBRA transmissionfor STA-3, STA-4, STA-5 and STA-6. After transmission of the COBRAschedule frame (not shown), the AP would transmit a first COBRAtransmission 215 to STA-1 and STA-2 and a second COBRA transmission 220to STA-3, STA-4, STA-5, and STA-6. If time remains in the COBRA period,and the frame exchanges of the previous COBRA schedule frame arefinished, the AP may schedule a new COBRA transmission between the APand a set of STAs. This set of STAs may or may not overlap with thepreviously scheduled STAs. While time remains in the COBRA period andall STAs on the COBRA schedule list have been communicated with orpolled, the AP may transmit a COBRA Period End frame and terminate theCOBRA period early. Alternatively, the AP may utilize the remaining timein the COBRA period to poll more STAs, which may not be included on theCOBRA schedule list, to determine whether the STAs have uplink trafficto transmit.

CSMA/CA contention window randomization and backoff procedures may notbe mandatory within the COBRA period. During a legacy period the AP mayhave data to transmit to another STA. As shown in FIG. 2, the AP hastraffic to transmit in the legacy period 230 to STA-7. The AP mayperform CSMA/CA to determine if the media is clear after the COBRAperiod 210 has expired. If the media is not clear, the AP may initiate abackoff procedure. The backoff procedure may also be initiated due to alack of an expected response due to certain rules, or due to extraprotection mechanisms to protect from interference of OBSS. In theexample shown in FIG. 2, the AP determines that the media is not clearand initiates a backoff procedure 235. When the backoff period ends andthe AP gains control of the media, the AP may transmit the datatransmission 240 to STA 7 according to the CSMA protocol. Although notshown in FIG. 2, if the media is not clear after backoff procedure 235,another backoff procedure may be performed.

Alternatively, the AP may want to perform COBRA transmission only whenthe AP acquires the media. If the AP does not dedicate or schedule COBRAtransmission in a beacon interval, the AP may need to compete with othernon-AP STAs to acquire the channel in order to perform COBRAtransmission. The other non-AP STAs may include both COBRA-capabledevices and non-COBRA capable or legacy devices that may not use COBRAto access the media. FIG. 4 is an example of Type II COBRA transmission.Type II COBRA transmission is a mechanism where the AP performs COBRAtransmission only when the AP acquires the media, i.e., the APsuccessfully competes with other non-AP STAs to acquire the channel. Asshown in FIG. 4, the AP has a COBRA transmission for STA-1 and STA-2 andanother COBRA transmission for STA-3, STA-4, STA-5 and STA-6. If themedia is not clear during the AP's first attempt to gain control of themedia, the AP performs backoff procedure 410. Once the AP has control ofthe media, the AP may perform a COBRA transmission 415 to a STA-1 and aSTA-2. After the transmission, the AP will again compete for the media.In this example, the media is busy during the AP's next attempt;therefore the AP performs another backoff procedure 420. Once the APagain gains control of the media, it may perform another COBRAtransmission 425 to STA-3, STA-4, STA-5 and STA-6. In Type II COBRAtransmission, the COBRA transmission may coexist with a CSMA/CA basedchannel access scheme, as shown. After COBRA transmissions 415 and 425are performed, the AP may perform CMSA/CA, which may include performinga backoff procedure 430 if the media is busy, and subsequentlytransmitting data 435 to the intended STA, i.e., STA-7, in accordancewith the CSMA protocol. Alternatively, the CSMA/CA based channel accessscheme may occur between the COBRA transmissions.

Multi-User Diversity in COBRA

COBRA may allow multiple STAs to communicate on multiple sub-channels atthe same time. In order to fully exploit the frequency selectivity andmulti-user diversity, each STA may transmit or receive data onsub-channels that have good channel quality. In other words, the channelselection for each communicating STA may be a function of the channelquality of the corresponding sub-channels.

FIG. 5 is a diagram of an example multi-user diversity and sub-channelselection procedure 500. In this example, the AP implicitly measures thechannel to schedule uplink transmissions for a plurality of STAs.Turning to FIG. 5, the AP may start a multi-user diversity enabled COBRAtransmission to a group of potential COBRA candidates, i.e., STA-1,STA-2, STA-3, . . . STA-N, to be scheduled for COBRA transmissions inthe uplink, by transmitting a sounding request frame 505. Although notshown, a similar procedure may be applied for scheduling downlinktransmissions. The sounding request frame may be used to solicit eachSTA to transmit a sounding frame to the AP, in order to estimate thewideband channel for each STA. The sounding request frame may includethe address of each STA, and in what order the STAs may transmitsounding frames. The AP may order the addresses of all STAs in thesounding request frame, such that the first addressed STA may transmit asounding frame in the first position, the second address STA maytransmit a sounding frame in the second position, and so on.

The AP may receive a sounding frame from each STA 510 included in thesounding request frame at a pre-determined timing. This may occur a SIFStime (or a new inter-frame space (IFS) time) later. For example, thefirst addressed STA may transmit a sounding frame in the first position;the second addressed STA may transmit a sounding frame in the secondposition, and so on. The sounding frame may be a null data packet (NDP),including only the preamble (for example, short training field, longtraining field, signaling field). The sounding frame may cover theentire frequency resource, e.g., the entire block of carriers, or theentire bandwidth. For example, although each STA may be scheduled foronly 20 MHz transmissions, each STA's sounding frame may span the entiresystem bandwidth supported by the AP, such as 80 MHz. Alternatively, thesounding frame may cover a portion of the frequency resource, e.g., adesired block of carriers by the STAs, or the assigned sub-channel(s).

Upon receiving the sounding frames from all STAs, the AP may estimatethe frequency domain channels for STA-1, STA-2, STA-3, . . . STA-N 515,across the entire system bandwidth supported by the AP. This may occur aSIFS time (or a new IFS time) later.

The AP may carry out an implementation-dependent module, to scheduledifferent users to different blocks of subcarriers 520. In one example,the AP may divide the entire system bandwidth into N blocks, such thatone STA may transmit on one block of subcarriers. In another example,the AP may divide the entire system bandwidth into M blocks (M<N), suchthat only M STAs may transmit, with each STA transmitting only on oneblock of subcarriers. The algorithm for implementing the scheduling ofdifferent users may be implementation-dependent.

Upon reaching a scheduling decision, the AP may transmit a schedulegrant frame 525, broadcasting the frequency allocation information toSTA-1, STA-2, STA-3, . . . STA-N. The scheduling grant frame may includethe address of each scheduled STA, together with the scheduling position(frequency band allocation information) of all the STAs. The schedulegrant frame may also serve as a synchronization frame. This may beachieved by including a preamble in the scheduling grant frame. Eachscheduled STA may use this preamble to perform proper timing adjustmentand frequency synchronization.

The AP may receive the multiple, orthogonal, COBRA transmissions fromthe multiple STAs 530, which transmit their respective packets, each attheir scheduled frequency position (block of subcarriers). This mayoccur a SIFS time (or a new IFS time) after the AP transmits theschedule grant frame.

The AP may then decode each received transmission separately, andperform a frame check sequence (FCS) for each STA 535. The AP maytransmit an ACK or NACK frame for each STA, with STA-1's ACK or NACKframe on the frequency band allocated to STA-1, STA-2's ACK or NACKframe on the frequency band allocated to STA-2, and so on.Alternatively, the AP may transmit an ACK or NACK frame for each STA ina single packet, for example, a primary band of the channel. This singlepacket may include the address of each STA, together with the ACK orNACK report corresponding to each STA.

FIG. 6 is a diagram of an example multi-user diversity and sub-channelselection procedure for a downlink transmission 600. In this procedure,the receivers, i.e., the STAs in the downlink, explicitly indicate thedesired resource to the transmitter, i.e., the AP. The procedure mayoccur in three phases, a wideband channel estimation phase, a feedbackphase and a multi-user diversity enabled COBRA transmission phase.

In the wideband channel estimation phase, the AP, at specific intervals,may broadcast wideband sounding frames spanning the entire bandwidth toa group of STAs (i.e., STA-1, STA-2, STA-3, . . . , STA-N) 605 to enablethe group of STAs to estimate the wideband channel. Alternatively, eachSTA may estimate the quality of each sub-band during normal transmissionfrom the AP to other STAs in the BSS.

In the feedback phase, the AP receives feedback from each STA regardingits desired channels for scheduling 610. The feedback may be the complexelements of the wideband channel. The AP may process the channelinformation to perform sub-channel selection 615. Alternatively, the STAmay perform the processing needed and feedback sub-channel informationthat is subsequently used by the AP for sub-channel selection. Thefeedback may depend on a specific sub-channel selection strategy. Forexample, using the Sum Best Improved (SBI) algorithm, assuming thechannel metric (CM) is the mean signal-to-noise-ratio (SNR), each STAmay feedback the mean SNR for each sub-channel. The STA may alsodetermine not to feedback its worst sub-channel. A feedback protocol maybe agreed on to enable proper feedback of the information needed.Alternatively, using the Sub Best (SB) algorithm, each STA may feedbackthe summation of the CM over the entire band. Assuming the CM is themean SNR, each STA may feedback the sum of mean SNRs over all sub-bands.

In one example, the AP may request the best N sub-channels from eachSTA. This may be implemented by a best-channel request frame that mayinclude the STA ID and the number of channels requested. The STA maytransmit a best channel response frame that includes the STA ID, and thechannels in the order of preference. For example, if N=3, the STA mayfeedback channels 4, 3 and 1. Alternatively, the AP may request for ablock feedback in which it polls each successive STA in the BSS. EachSTA may also feedback a CM or combination of CMs indicating the level ofpreference. This may be the SNR/SINR of the sub-channel, theinterference level experienced in the sub-channel, the number ofcollisions experienced in the sub-channel, the channel energy, and thelike.

In another example, each STA may feedback a differential metric framethat indicates the difference of a desired metric between the primarysub-channel and all other sub-channels or the correlation between themetric in a primary sub-channel and other sub-channels. This may enablethe AP to estimate the channel quality of the rest of sub-channels giventhe observation of the primary sub-channel. The metric may be theSNR/SINR of the sub-channel, the interference level experienced in thesub-channel, the number of collisions experienced in the sub-channel,the channel energy, and the like. In this example, the metric for theprimary channel may be fed back at intervals decided by the AP. Thedifferential metric frame may be fed back at longer intervals. This maybe at periodic intervals or when a differential metric change exceeds athreshold. The AP may then use a combination of the relative strength ofthe metric on the primary channel for the different STAs combined withthe differential information for each STA in its scheduling decision.This may enable more efficient feedback for the system.

In the multi-user diversity enabled COBRA transmission phase, uponreaching a scheduling decision, the AP may transmit a schedule grantframe 620 to the group of STAs, broadcasting the frequency allocationinformation. The scheduling information may be based on full or partialinformation. The schedule grant frame may include the address of eachscheduled STA, together with the scheduling position (frequency bandallocation information) of the STAs. The schedule grant frame may alsoserve as a synchronization frame. This may be achieved by including apreamble in the schedule grant frame. Each scheduled STA may use thispreamble to perform proper timing adjustment and frequencysynchronization. It should be noted that the AP may send a single grantframe to all STAs or may send multiple schedule grant frames to eachindividual STA.

The AP may transmit packets to the group of STAs, each at its scheduledfrequency position (block of subcarriers or sub-channel) 625. This mayoccur a SIFS time (or a new IFS time) after the AP transmits theschedule grant frame. The AP may receive acknowledgements from the groupof STAs if the transmitted packets are or are not successfully received.The acknowledgements may be ACK frames, NACK frames, or block ACKframes. The AP may receive the acknowledgement frames from multiple STAssimultaneously and the STAs may be separated in frequency or codedomain. Alternatively, the AP may receive the acknowledgement framessequentially one after another. In the second method, the AP may or maynot need to poll the STAs for the acknowledgement frames.

FIG. 7 is a diagram of an example multi-user diversity and sub-channelselection procedure for an uplink transmission 700. The procedure mayoccur in three phases, a wideband channel estimation phase, a feedbackphase and a multi-user diversity enabled COBRA transmission phase.

In the wideband channel estimation phase, the AP may transmit soundingrequest frames to each STA 705, as described above, to enable the AP toestimate the best uplink channel. The sounding request frame may be usedto solicit each STA to transmit a sounding frame to the AP, in order toestimate the wideband channel for each STA. The sounding request framemay include the address of each STA, and in what order the STAs maytransmit sounding frames.

In the feedback phase, each STA that is included in the sounding requestframe may respond with a sounding frame, at a pre-determined time 710.This may occur a SIFS time (or a new IFS time) after receiving thesounding request frame from the AP. The sounding frame may be a nulldata packet, including only the preamble (for example, short trainingfield, long training field, signaling field) and may cover the entireblock of carriers. For example, although each STA may be scheduled foronly 20 MHz transmissions, each STA's sounding frame may span the entiresystem bandwidth supported by the AP, for example, 80 MHz. The soundingframe may also cover the desired block of carriers by the STAs. The APmay estimate the frequency domain channels for all STAs 715, across theentire system bandwidth supported by this AP.

Alternatively, the AP may use the information gleaned from downlinktransmission estimation and feedback in scheduling uplink transmission(for example, assume channel reciprocity in which the best channel fordownlink transmission is the best channel for uplink transmission). TheSTA may be using information from downlink channel estimation (forexample, reciprocity) and may transmit an indicator frame on the desiredsub-channel as an indication of the best channel in the multi-userdiversity sense. For example, the indicator frame may be arequest-to-send (RTS) frame.

In the multi-user diversity enabled COBRA transmission phase, uponreaching a scheduling decision, the AP may transmit a schedule grantframe 720 to the group of STAs, broadcasting the frequency allocationinformation. The scheduling information may be based on full or partialinformation. The schedule grant frame may include the address of eachscheduled STA, together with the scheduling position (frequency bandallocation information) of the STAs. The schedule grant frame may alsoserve as a synchronization frame. This may be achieved by including apreamble in the schedule grant frame. Each scheduled STA may use thispreamble to perform proper timing adjustment and frequencysynchronization.

All of the scheduled STAs may then transmit packets, each at itsscheduled frequency position (block of subcarriers). The AP may receivethe multiple, orthogonal, COBRA transmissions from the multiple STAs725. This may occur a SIFS time (or a new IFS time) after the schedulegrant frame is received by the STAs. The AP may decode the transmissionsseparately and may perform FCS checks for each STA 730. The AP maytransmit an ACK or NACK frame for each STA, for example, with STA-1'sACK or NACK frame on the frequency band allocated to STA-1, STA-2's ACKor NACK frame on the frequency band allocated to STA-2, and so on.Alternatively, the AP may transmit an ACK or NACK frame for each STA ina single packet, for example, on a primary band of the channel. Thissingle packet may include the address of each STA, together with theACK/NACK report corresponding to each STA.

In order to perform either implicit multi-user diversity or explicitmulti-user diversity, channel measurements may be necessary. Withimplicit multi-user diversity, the AP may measure the channel and themeasurements it utilizes may be implementation dependent. With explicitmulti-user diversity, the non-AP STAs may perform measurements on thedownlink channel, and feedback the measurements to the AP, and thus,channel measurements may need to be specified in the standards. The CMmay be represented by a mean SNR, harmonic mean SNR, or channel capacityover a sub-channel.

Exemplary CM definitions will now be described.

In a single data stream case, the measurements may be mean SNR, harmonicmean SNR, and channel capacity.

For any STAi, the mean SNR for the n^(th) sub-channel may be defined as:

$\begin{matrix}{{{Mean\_ SNR}_{i,n} = {\frac{1}{K}{\sum_{k = 0}^{K - 1}{SNR}_{i,n,k}}}},{i = 0},1,\ldots\mspace{14mu},{N - 1},{n = 0},1,\ldots\mspace{14mu},{N - 1}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where SNR_(i,n,k) is the SNR of the k^(th) subcarrier for STAi in then^(th) sub-channel, N is the number of total available sub-channels andK is the number of subcarriers in each sub-channel.

For any STAi, the harmonic mean SNR for the n^(th) sub-channel may bedefined as:

$\begin{matrix}{{{{Harmonic\_ Mean}{\_ SNR}_{i,n}} = \left( {\frac{1}{K}{\sum_{k = 0}^{K - 1}\frac{1}{{SNR}_{i,n,k}}}} \right)^{- 1}},{i = 0},1,\ldots\mspace{14mu},{N - 1},{n = 0},{1\ldots}\mspace{14mu},{N - 1.}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

For any STAi, the channel capacity for the n^(th) sub-channel may bedefined as:

$\begin{matrix}{{C_{i,n} = {\frac{1}{K}{\sum_{k = 0}^{K - 1}{10\log\; 2\left( {1 + {H_{i,n,k}}^{2}} \right)}}}},} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where H_(i,n,k) is the equivalent channel frequency response at thek^(th) subcarrier for STAi in the n^(th) sub-channel.

In a multi data stream case, assuming transmitter and receiver antennasare N_(tx) and N_(rx), respectively and the number of data streams,N_(ss) is equal to the minimum of N_(tx) and N_(rx), two measurementsmay be used: post processed mean SINR and channel capacity.

For any STAi, the post processed mean SINR for the n^(th) sub-channelmay be defined as:

$\begin{matrix}{{{SINR}_{i,n} = {\frac{1}{K}{\sum_{k = 0}^{K - 1}{SINR}_{i,n,k}}}},} & {{Equation}\mspace{14mu} 4}\end{matrix}$

where SINR_(i,n,k) is the SINR of the k^(th) subcarrier for STAi in then^(th) sub-channel and may be obtained by:

$\begin{matrix}{{{SINR}_{i,n,k} = {\frac{1}{N_{ss}}{\sum_{N_{ss} = 0}^{N_{ss} - 1}\frac{P_{n_{ss}}}{I_{n_{ss}} + N_{0,n_{ss}}}}}},} & {{Equation}\mspace{14mu} 5}\end{matrix}$

where P_(n) _(ss) is the power of the (n_(ss))^(th) data stream, I_(n)_(ss) is the total interference from other data streams to the(n_(ss))^(th) data streams and N_(0,n) _(ss) may be the related noisepower.

For any STAi, the channel capacity for the n^(th) sub-channel may bedefined as:

$\begin{matrix}{C_{i,n} = {\frac{1}{K}{\sum_{k = 0}^{K - 1}{10\log\; 2\left( {1 + {\left( H_{i,n,k} \right)^{H}H_{i,n,k}}} \right)}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

where H_(i,n,k) with demision of N_(rx)×N_(tx) is the frequency domainchannel response for the i^(th) user at the k^(th) subcarrier in n^(th)sub-channel.

In order to achieve more frequency diversity, once STAs (e.g., COBRAusers) are selected by grouping algorithms, the AP may need to choosethe right sub-channel for the STAs according to the channelmeasurements.

Exemplary sub-channel selection strategies, for example the sum best(SB) algorithm, the sum best improved (SBI) algorithm, or the each bestimproved (EBI) algorithm, will now be described. Note, although CM maybe utilized in the algorithms, any one of the metrics describedheretofore or known to those of skill in the art may be used. Forexample, CM may be replaced by Mean_SNR, Harmonic_Mean_SNR, Mean_SINR,Harmonic_Mean_SINR or Capacity.

If all the users are experiencing similar delay spread channels, or ifthe AP has no knowledge of the channel delay spread, based on themeasurements defined above, SNR, SINR or capacity, (SNR is used as anexample below), the SB algorithm, SBI algorithm, or EBI algorithm, asdefined below may be used.

In the SB algorithm, the sub-channel allocation may be obtained byfinding the maximum of the sum SNR of all users:

$\begin{matrix}{{\left\{ {n_{0},n_{1},\ldots\mspace{14mu},n_{I - 1}} \right\} = {\arg\mspace{14mu}{\max\limits_{{n_{i} \in 0},1,\ldots\mspace{14mu},{N - 1}}{\sum_{i = 0}^{I - 1}{CM}_{i,n_{i}}}}}},{w.r.},{n_{i} \neq n_{j}},{{{if}\mspace{14mu} i} \neq j}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

where n₁ is the index of the sub-channel allocated to the i^(th) user.Table 1 is an example of assigning four sub-channels to four STAs basedon SNR. Each STA may have four options and the same sub-channel may notbe allocated to more than one STA, therefore, in this example, there maybe 24 selection combinations. Among all the 24 combinations, the one{n₀, n₁, n₂, n₃}={2, 1, 3, 4} with the maximum SNR:

$\begin{matrix}{{{{SNR}_{1,2} + {SNR}_{2,1} + {SNR}_{3,3} + {SNR}_{4,4}} = {\max\limits_{{n_{i} \in 0},1,2,3}{\sum_{i = 0}^{3}{SNR}_{i,n_{i}}}}},{s.t.},{n_{i} \neq n_{j}},{{{if}\mspace{14mu} i} \neq j}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

may be selected as the optimum solution as shown in bold in Table 1,below.

TABLE 1 EXAMPLE SUB-CHANNEL ALLOCATION FOR FOUR (4) STAS Sub Sub Channel1 Sub Channel 2 Sub Channel 3 Channel 4 STA 1 SNR_(1,1) SNR_(1,2)SNR_(1,3) SNR_(1,4) STA 2 SNR_(2,1) SNR_(2,2) SNR_(2,3) SNR_(2,4) STA 3SNR_(3,1) SNR_(3,2) SNR_(3,3) SNR_(3,4) STA 4 SNR_(4,1) SNR_(4,2)SNR_(4,3) SNR_(4,4)

In the SBI algorithm, in addition to maximizing the sum SNR of all STAs,no STA may be assigned with that STA's worst sub-channel:

$\begin{matrix}{{\left\{ {n_{0},n_{1},\ldots\mspace{14mu},n_{N - 1}} \right\} = {\arg{\max\limits_{n_{i}}{\sum_{i = 0}^{N - 1}{CM}_{i,n_{i}}}}}},{w.r.},\left\{ \begin{matrix}{{n_{i} \neq n_{j}},{{{if}\mspace{14mu} i} \neq j}} \\{{CM}_{i,n_{i}} > {\min\left\{ {{CM}_{i,n},{n = 0},1,\ldots\mspace{14mu},{N - 1}} \right\}}}\end{matrix} \right.} & {{Equation}\mspace{14mu} 9}\end{matrix}$

If all STAs have the same worst sub-channel, the STA with the maximumSNR at the worst sub-channel among all the STAs may be allocated thesub-channel.

For the EBI algorithm, in addition to maximizing the sum SNR of all STAsand avoiding assigning a STA with its worst sub-channel, the EBIalgorithm may schedule at least one of the STAs with its bestsub-channel:

$\begin{matrix}{{\left\{ {n_{0},n_{1},\ldots\mspace{14mu},n_{N - 1}} \right\} = {\arg{\max\limits_{n_{i}}{\sum_{i = 0}^{N - 1}{CM}_{i,n_{i}}}}}}{{w.r.},\left\{ \begin{matrix}{{n_{i} \neq n_{j}},{{{if}\mspace{14mu} i} \neq j}} \\{{CM}_{i,n_{i}} > {\min\left\{ {{CM}_{i,n},{n = 0},1,\ldots\mspace{14mu},{N - 1}} \right\}}} \\{\left\{ {{CM}_{i,n_{i}} > {\max\left\{ {{CM}_{i,n},{n = 0},1,\ldots\mspace{14mu},{N - 1}} \right\}}} \right\} \neq \varnothing}\end{matrix} \right.}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

If all the STAs are experiencing different delay spread channels, andthe AP has some knowledge of the channel delay spread, the sub-channelselection strategy may be STAs with different delay spread channels mayexpect different sub-channel selection gain. In order to maximize thetotal throughput of COBRA transmission over all the STAs, the AP mayselect the best channel for the STA with maximum sub-channel selectiongain. Then, select the second best channel for the STA with secondmaximum sub-channel selection gain, and so on.

FIG. 8 is a diagram of an example downlink COBRA-capable transmitter800. The transmitter may include a MAC interface 805, and one or moreprocessing units 810 a-n. The number of processing units may be based onthe number of STAs in the COBRA system, and each of the STAs may beassigned a processing unit. Each processing unit 810 a-n may include aPHY padding unit 815, a scrambler unit 820, and encoder unit 825, aninterleaving unit 830, and a constellation mapping unit 835. The MACinterface 805 may prepare the traffic to be transmitted to the multipleSTAs i.e., STAs 1-4, and passes them to the one or more processing units810 a-n, which may be in the PHY layer. For each data stream for eachSTA, padding may be performed at the PHY padding unit 815, scramblingmay be performed at a scrambler unit 820, encoding may be performed atthe encoder unit 825, interleaving may be performed at the interleavingunit 830 and constellation mapping may be performed at the constellationmapping unit 835. Based on the multi-user sub-channel selectionalgorithm, the AP may map data streams from multiple STAs to theselected sub-channels 840 a-n. Then, a wideband inverse discrete Fouriertransform (IDFT) may be applied for the entire frequency band and GIsmay be added at a wideband IDFT/GI adder unit 845. The resulting dataflow will be transmitted to the RF frontend 850 for transmission.

FIG. 9 is a diagram of an example downlink COBRA-capable receiver 900for STA k. The downlink COBRA-capable receiver 900 may include anantenna 905 and a processing unit 910. The processing unit 910 mayinclude a start-of-packet (SOP) detection unit 915, a GI removal unit920, a wideband discrete Fourier transform (DFT) unit 925, a frequencyband mapping unit 930, a channel estimation (CHEST) unit 935, anequalizer 940, a demapping and deinterleaving unit 945, and a decoder950. The procedure for STA k may begin with the reception of thewideband signal (for example, the signal across the entire transmittedbandwidth) at the antenna 905, which may be followed by the procedurefor start-of-packet (SOP) detection at the SOP detection unit 915. Theguard interval may be removed at the GI removal unit 920, followed by awideband DFT operation at the wideband DFT unit 925. According to theframe exchange before the COBRA session, the AP may signal thesub-channel allocation for this COBRA session. Therefore, STA k mayperform frequency band mapping at the frequency band mapping unit 930and acquire the frequency band signal on its allocated sub-channel(s).This may be followed by channel estimation at the CHEST unit 935,equalization at the equalizer 940, demapping and deinterleaving at thedemapping and deinterleaving unit 945, and decoding at the decoder 950.

Simulations to demonstrate the relative performance of the sub-channelselection algorithms described above in an 802.11 system with a singleBSS operating on an 80 MHz bandwidth will now be described. In thesimulations, the AP may operate on an 80 MHz channel and transmit to andreceive from four STAS through COBRA transmission. Each STA may beallocated a 20 MHz sub-channel. The same modulation and coding scheme isassumed for all the STAs. MCS5, which refers to 64 QAM and rate 2/3convolutional code, may be utilized in all the simulations.

Two simulation scenarios may be defined. In the first simulationscenario, a single data stream may be transmitted to and received fromeach STA. Thus N_(ss)=1, where N_(ss) stands for the number of datastreams. Packet size may be 500 bytes. A single antenna may be utilizedat both the AP side and STAs side. In the second simulation scenario,two data streams may be transmitted to and received from each STA, thusN_(ss)=2. Packet size is 1000 bytes. Both AP and STAs may have twoantennae.

Channel models utilized in the simulations may be IEEE 802.11 Channel Band Channel D with root mean square (RMS) delay spread of 15 ns and 50ns respectively. Both channel models may represent indoor multipathsituations. Due to the difference of RMS delay spread, channel D may bemore frequency selective than channel B. In addition, random angle ofarrivals (AoAs) and random angle of departures (AoDs) may be chosen fordifferent STAs.

In the first simulation scenario, the single data stream case, all thechannel metrics may perform in a similar way since they are functions ofabsolute value of channel coefficients in the frequency domain. Thus,only simulation results using channel metric Mean_SNR may be shown. Inthe second simulation scenario, where multiple data stream transmissionis involved, MIMO channels may be more complicated and many factors maycontribute to the final PER vs SNR results, such as absolute value ofchannel coefficients, condition number of the channel matrix, and thelike. The three channel metrics may perform slightly different, howeverMean_SNR and Harmonic_Mean_SNR may perform in a similar way.

In order to fully evaluate the proposed sub-channel selection algorithmsand COBRA scheme, two benchmark systems may be considered. In benchmarksystem I, COBRA transmission to four STAs with random sub-channelselection may be used, for example, without sub-channel selectionalgorithms being applied. In benchmark system II, traditional single STAtransmission on an 80 MHz channel may be used. In order to compare theCOBRA transmissions, 4 times packet size may be used, for example, 2000bytes for simulation scenario 1 and 4000 bytes for scenario 2. In thisway, the total amount of data payload may be the same for all theschemes.

It may be assumed that the channel is static; therefore the channel usedfor COBRA data transmission may be the same as that used for sub-channelselection. The AP may have channel state information of all the usersand may perform sub-channel selection algorithms.

FIG. 10 is a graphical representation of simulation results ofmulti-user sub-channel selection with simulation scenario 1 with onedata stream transmission in both channel B and channel D. Simulationsusing the SB, SBI, and EBI sub-channel selection algorithms and withoutusing sub channel selection are shown. The graph shown in FIG. 10includes an axis representing the packet error rate (PER) and an axisrepresenting SNR measured in decibels (dB). As shown in FIG. 9, the SBIscheme and the EBI scheme perform almost identically. The SBI and EBIschemes are slightly better than that of the SB scheme. As describedabove, an advantage of SBI and EBI schemes may be to avoid the worstchannel for all the users. According to the simulation results, at 1%PER level, proposed sub-channel selection algorithms show 3 to 4 dB gainin channel D and 5 to 6 dB gain in channel B compared to the Benchmarksystem I where no sub-channel selection algorithm applied.

Sub-channel selection gain in channel B is more significant than that inchannel D. Channel D may be more frequency selective than channel B inthe sub-carrier level. However, if the Mean_SNR on a 20 MHz sub-channelis used as a measurement, the channel variation of channel B may be moresignificant than that of channel D. This observation may depend on thesize of sub-channel. If the size of sub-channel is continually reduced,the channel variation in channel D, in the sub-channel level, mayincrease and exceed that in Channel B eventually.

FIG. 11 is a graphical representation of an empirical cumulativedistribution function (CDF) of channel magnitude difference oversub-channels. The graph shown in FIG. 11 includes an axis representingthe CDF and an axis representing the channel magnitude difference. FIG.11 confirms the above observation. The average SNR on each sub-channelmay be calculated, and then the difference of maximum SNR and minimumSNR may be recorded. The curves of simple exponential multipath fadingchannels with RMS delay spread 0 ns, 10 ns, 50 ns and 100 ns,respectively, may be obtained and are shown in FIG. 10. The simulationsshown in FIG. 11 are with an 80 MHz channel. With a 256 sub-channelcase, each sub-channel may contain one sub-carrier. While in the 4sub-channel case, each sub-channel is 20 MHz wide, and may contain 64sub-carriers. According to this observation, with a 20 MHz sub-channelresolution, the multi-user sub-channel diversity may be more significantin the channels with relatively smaller RMS delay spread.

Compared to the benchmark system II, in which the AP transmits to oneuser using an 80 MHz channel, based on FIGS. 10-11, the proposed COBRAscheme with the sub-channel selection algorithm SBI or EBI is 2 dBbetter in channel B, and 1.2 dB better in channel D. Narrow bandinterference is not considered in the simulation. If however narrow bandinterference was to be considered, more significant performance gainsmay have been observed by using COBRA sub-channel selection.

FIG. 12 is a graphical representation of simulation results ofmulti-user sub-channel selection with two data stream transmission overchannel B with simulation scenario 2, the two data stream case. In thetwo data stream transmission case, due to the inter-stream interference,the post processed SINR may be utilized as a basic unit to calculateMean_SINR and Harmonic_Mean_SINR. On each sub-carrier, post SINR may becalculated after minimum mean square error (MMSE) equalization at the APside. Simulations using both capacity based and SINR based SB, SBI, andEBI sub-channel selection algorithms and without using sub channelselection are shown. The graph shown in FIG. 12 includes an axisrepresenting PER and an axis representing SNR measured in dB. Referringto FIG. 12, as in the single data transmission case, SBI and EBI mayperform almost the same and slightly better than SB. Capacity basedsub-channel selection algorithms may be slightly better than SINR basedsub-channel selection algorithms. Utilizing the sub-channel selectionalgorithm may result in some gain compared to benchmark system I.However, the gain may be less than that observed with single datatransmission. Compared to benchmark system II, where COBRA is notutilized and transmission is over the 80 MHz channel, capacity basedsub-channel selection algorithms with SBI/EBI show a small gain at onepercent PER. Other algorithms may perform similarly or slightly worsethan the 80 MHz transmission. This may be reasonable because with twodata stream transmission the 2×2 channel matrix (H) determines theperformance. Thus, the spatial domain diversity contributes to the finalresults. Taking the 2×2 spatial diversity into consideration, thefrequency diversity over the entire frequency band may become less whencompared to the previous case, i.e., a 1×1 channel.

FIG. 13 is a graphical representation of simulation results ofmulti-user sub-channel selection with two data stream transmission overchannel D with simulation scenario 2, the two data stream case.Simulations using both capacity based and SINR based SB, SBI, and EBIsub-channel selection algorithms and without using sub channel selectionare shown. The graph shown in FIG. 13 includes an axis representing PERand an axis representing SNR measured in dB. In this example, thecapacity based algorithms may be slightly better than SINR basedalgorithms. Performing sub-channel selection may be better than notperforming sub-channel selection. Compared to non-COBRA transmissionover the entire 80 MHz channel, the COBRA scheme with capacity basedsub-channel selection algorithm SBI/EBI may be slightly better.

Methods to Improve COBRA Efficiency

With normal WiFi systems, the AP and non-AP STAs may have the samepriority to compete and acquire the media. When the AP needs to competewith other STAs to acquire the channel, it may be unfair and inefficientfor COBRA transmissions. STAs may need to wait for the AP to scheduleDL/UL COBRA transmissions and the AP may need to compete with the restof the STAs to acquire the channel in order to do so. For example, theBSS may have N COBRA capable STAs and N non-COBRA capable STAs. The APmay be competing with N non-COBRA capable STAs, and the chance for COBRAtransmission may only be 1/(N+1). Therefore a COBRA capable STA may have1/[(N+1)N] chance to receive/transmit. Therefore, in order to fully takethe advantages of COBRA transmission, an access scheme to improve thechannel access fairness and efficiency for COBRA transmission isdesired.

Channel access fairness and efficiency for COBRA transmissions may beimproved by extending the transmission time or traffic opportunity(TXOP) for COBRA capable STAs once the AP obtains the channel. Theconcept of TXOP may be introduced as the basic unit of allocation of theright to COBRA transmissions.

COBRA TXOP may be defined by a starting time and a maximum length. TheCOBRA TXOP may be obtained by the AP winning the channel, then the APmay schedule either DL or UL COBRA transmissions for COBRA capable STAs.Multiple frames may be transmitted during a COBRA TXOP to multiple COBRAcapable STAs. These frames may be transmitted to multiple COBRA capableSTAs at the same time, at a nearly identical time, or at a staggeredtime. The AP or COBRA capable STAs may commence transmission ofadditional frames SIFS after the completion of the current frameexchange sequence, if the duration of transmission of that frame plusany expected acknowledge for that frame is less than the remaining TXNAVtimer value.

COBRA TXOP transmission procedures may include two phases: COBRA TXOPinitiation phase and COBRA multi-user multi-frame transmission phase. Inthe COBRA TXOP initiation phase, the COBRA TXOP may be initiated by anAP. The COBRA TXOP limit duration may be advertised by the AP in a COBRAparameter set element in a beacon or probe response frame transmitted bythe AP. After acquiring the channel, the AP may initiate the COBRA TXOPusing COBRA DL/UL schedule frames, a COBRA RTS frame or a group RTS(G-RTS) frame), a COBRA CTS frame transmitted to itself, a COBRAmanagement frame or MU-PCA management frame, and the like.

In the COBRA multi-user multi-frame transmission phase, the COBRAmulti-user multi-frame transmission may occur after the AP acquires themedia and initiates the COBRA TXOP. The transmission rules of the COBRATXOP may follow the normal 802.11 TXOP transmission rules. For example,the AP may assign different MCSs to different STAs on differentsub-channels. The AP may also assign different numbers of data streamsto different STAs on different sub-channels. The AP may also usedifferent spatial technologies on different STAs on differentsub-channels (for example, some STAs may utilize space-time block code(STBC), while other STAs may utilize spatial multiplexing). MU-MIMO maybe combined with COBRA. For example, the AP may perform MU-MIMO onsub-channel 1 to multiple STAs. The AP may also utilize differentchannel coding schemes for different STAs on different sub-channels.Different traffic access categories (AC) may also be allowed to transmitover one COBRA TXOP.

In the examples provided herein, it should be noted that the number ofSTAs depicted are not intended to be limiting. The examples are providedonly for illustrative purposes. Any number of STAs, including additionalor less than those depicted in the examples may perform the methods andprocedures set forth herein. In addition, the operating channels andallocated frequencies in the examples provided herein are also notintended to be limiting and are provided only for illustrative purposes.For example, the AP may allocate frequency portions, channels, orsub-channels to STAs as described above. The channels may be contiguousor non-contiguous. The carrier blocks (or sub-channels) may be localizedor distributed. In addition the STA and AP may operate on variousfrequencies and channels, as described above.

FIG. 14 is a diagram of an example DL COBRA TXOP 1400. In this example,an AP 1405, a STA-1 1410, and a STA-2 1415 are shown. The AP 1405 may beoperating on a 40 MHz channel, which may include two 20 MHzsub-channels. It should be noted that this is for illustrative purposesonly and the AP may be operating on any channel size or configuration.Once the AP 1405 acquires the channel, the AP 1405 may assign STA-1 1410to the first 20 MHz sub-channel and STA-2 1415 to the second 20 MHzsub-channel. The AP may assign the channels in accordance with theprocedures described above. The AP 1405 may transmit COBRA scheduleframe 1420 a to STA-1 1410 and COBRA schedule frame 1420 b to STA-2 1415on their respective 20 MHz sub-channels. The COBRA schedule frames 1420a, 1420 b may be repeated with or without phase rotation on all of thesub-channels. In order to make the transmission of the COBRA scheduleframes 1420 a, 1420 b reliable, the AP 1405 may utilize a lower MCS.STA-1 1410 and STA-2 1415 may confirm by transmitting ACK frames 1430 a,1430 b to the AP 1405 on their assigned sub-channels. This exchangebetween the AP 1405 and STA-1 1410 and STA-2 1415 of COBRA scheduleframes 1420 a, 1420 b and ACK frames 1430 a, 1430 b may be consideredthe COBRA TXOP initiation phase. The duration field of the frames usedto initiate the COBRA TXOP, the COBRA schedule frames and the followingACK frames in this example, may be set to cover the entire TXOP.Alternatively, the AP may reset the NAV by utilizing the duration fieldon each frame transmitted within the TXOP. Once the COBRA TXOPinitiation phase is complete, the AP 1405 may commence the COBRAmulti-user multi-frame transmission phase by transmitting DL packets1435 a, 1435 b to STA-1 1410 and STA-2 1415, respectively. As shown inFIG. 14, the DL data packet 1435 a intended for STA-1 1410 is largerthan the DL packet 1435 b intended for STA-2 1415. The AP 1405 may padzeroes in the tail of DL packet 1435 b to align the packet size with DLpacket 1435 a in order to keep control of the TXOP over allsub-channels. STA-1 1410 and STA-2 1415 may confirm by transmitting ACKframes 1440 a, 1440 b to the AP 1405 on their assigned sub-channels.This process continues until the TXOP is complete, e.g., more datapackets may be transmitted in a similar fashion until the TXOP ends. Itshould be noted that the packets transmitted within a TXOP are typicallyseparated by a small time duration, such as SIFS, so that the unintendedSTAs may not have a chance to break the TXOP. A SIFS is used forillustrative purposes only, and additional time durations may also beused.

FIG. 15 is a diagram of an example UL COBRA TXOP 1500. In this example,an AP 1505, a STA-1 1510, and a STA-2 1515 are shown. As in the DL COBRATXOP, the AP 1505 may be operating on a 40 MHz channel, which mayinclude two 20 MHz sub-channels. It should be noted that this is forillustrative purposes only and the AP may be operating on any channelsize or configuration. Once the AP 1505 acquires the channel, it mayassign the two sub-channels to STA-1 1510 and STA-2 1515, respectively.To assign the two sub-channels, the AP 1505 may perform a pollingprocedure. The AP 1505 may transmit COBRA polling frame 1520 a to STA-11510 and COBRA polling frame 1520 b to STA-2 1515 on their assigned 20MHz sub-channels. STA-1 1510 and STA-2 1515 may each transmit ACK frames1530 a, 1530 b to the AP 1505. The ACK frames 1530 a, 1530 b may containthe corresponding uplink traffic information, such as packet length, QoSrequirements and the like. After receiving the ACK frames 1530 a, 1530b, the AP 1505 may transmit COBRA schedule frames 1535 a, 1535 b toSTA-1 1510 and STA-2 1515. The COBRA schedule frames 1535 a, 1535 b mayannounce the maximum packet size of the upcoming uplink COBRAtransmissions, and packet sizes of each STA. The exchange of COBRApolling frames, ACKs, and COBRA schedule frames may be considered theCOBRA TXOP initiation phase in the uplink. The duration field of theframes used to initiate the COBRA TXOP, COBRA polling frames andcorresponding ACK frames in this example, may be set to cover the entireTXOP. Alternatively, the AP 1505 may reset the NAV by utilizing theduration field on each frame transmitted within the TXOP. Once the COBRATXOP initiation phase is complete, STA-1 1510 and STA-2 1515 maycommence the COBRA multi-user multi-frame transmission phase bytransmitting UL data packets 1540 a, 1540 b to AP 1505. As shown in FIG.15, STA-2 1515 transmits relatively smaller packets to the AP 1505 whencompared to the maximum packet size. As a result, STA-2 1515 may padzeroes to the tail of the packet to align the packet size with that ofother STAs, here STA-1 1510. If padding is not performed, it may bedifficult for the AP 1505 to keep the control of the TXOP over all thesub-channels. If the AP 1505 receives UL data packets 1540 a and 1540 b,the AP 1505 may transmit an ACK with the next COBRA schedule frames 1545a, 1545 b to STA-1 1510 and STA-2 1515. Although not shown in thisexample, the AP may alternatively transmit an ACK without the next COBRAschedule frames. In this case, the AP may perform another pollingprocedure or terminate the TXOP.

At least two different types of COBRA schedule frame formats may beused. For example, the COBRA schedule frame may contain information ofseveral upcoming packets or all the transmission packets within thewhole TXOP. In this case, the AP may transmit an ACK to each STA aftersuccessfully receiving the packet or transmit a NACK if failing toreceive the packet. In another example, the COBRA schedule frame mayonly contain the information of upcoming packets. As a result, the ACKor NACK may be transmitted back with the next COBRA schedule frame asshown in FIG. 15 and as described above.

In existing WLAN TXOP systems, a STA may perform a point coordinationfunction inter-frame space (PIFS) recovery or a backoff as a response toa transmission failure within a TXOP. In this way, a STA which is notinvolved in the TXOP transmission may not be able to interrupt theexisting TXOP, since it has to wait a distributed inter-frame space(DIFS) before it may perform normal backoff for contention. Forreference, a DIFS is longer than PIFS. With COBRA transmissions, the APmay schedule multiple users to share the entire bandwidth in thefrequency domain. For example, each STA may be allocated to one or moresub-channels. Therefore, the AP may intend to maintain the continuity ofCOBRA TXOP transmissions over all of the sub-channels. With current WLANsystems, devices may not be able to transmit and receive simultaneously,for example, the AP may not be able to begin a new transmission to oneSTA on one or more sub-channels while another STA is transmitting an ACKback to the AP. As a result, using a PIFS recovery to maintain the TXOPmay not be possible with respect to a COBRA TXOP. Thus, procedures tocombat transmission failures in COBRA TXOPs are desirable.

Transmission failures may occur in the DL COBRA TXOP. For example, inthe COBRA TXOP initiation phase, one or more STAs may not receive theCOBRA schedule frame, due to poor channel status or interference. Inaddition, the COBRA schedule frame may not be received if a STA is outof scope. In the COBRA transmission phase, the downlink transmission inone or more sub-channels within the TXOP may fail. Similarly,transmission failures in UL COBRA may be the result of a STA failing toreceive the COBRA poll frame transmitted by the AP due to channelstatus. The STA may also fail to receive the COBRA poll frame if the STAis out of scope. The STA may also fail to receive a COBRA schedule framefrom the AP in COBRA UL. Additionally, an uplink transmission in certainsub-channels within a TXOP may fail.

NACK frames and several procedures which may be utilized in COBRA TXOPto address the transmission failures and maintain the COBRA TXOP willnow be described.

FIG. 16 is a diagram of an example transmission failure of COBRAschedule information in DL COBRA 1600. In this example, an AP 1605, aSTA-1 1610, a STA-2 1615 and a STA-3 1620 are shown. The AP 1605 may beoperating on a 40 MHz channel, which may include two 20 MHzsub-channels. It should be noted that this is for illustrative purposesonly and the AP may be operating on any channel size or configuration.Once the AP 1605 acquires the channel, the AP 1605 may assign STA-1 1610to the first 20 MHz sub-channel and STA-2 1615 to the second 20 MHzsub-channel. The AP may assign the channels in accordance with theprocedures described above. The AP 1605 may transmit COBRA scheduleframe 1625 a to STA-1 1610 and COBRA schedule frame 1625 b to STA-2 1615on their respective 20 MHz sub-channels. After a SIFS, the AP 1605receives an ACK 1635 a from STA-1, but fails to receive an ACK 1635 bfrom STA-2 1615. As a result, the AP 1605 may retransmit COBRA scheduleframe 1640 a to STA-1 1610 and COBRA schedule frame 1640 b to STA-21615. If the AP 1605 receives an ACK 1645 a from STA-1 1610, but againfails to receive an ACK 1645 b from STA-2 1615 before the retransmissiontime achieves the maximum predetermined value, the AP 1605 may choose toschedule the sub-channel previously assigned to STA-2 1615 to anotherSTA, here STA-3 1620, by transmitting COBRA schedule frame 1650 a toSTA-1 1610 and COBRA schedule frame 1650 b to STA-3 1620. Upon receivingan ACK 1660 a, 1660 b from both STAs, the AP 1605 may transmit DL datapacket 1670 a to STA-1 1610 and DL data packet 1670 b to STA-3 1620. TheAP 1605 may pad zeroes in the tail of DL data packet 1670 b intended forSTA-3 1620 to align the packet size with DL data packet 1670 a intendedfor STA-1 1610 in order to keep control of the TXOP over allsub-channels. It should be noted that the AP may perform more or lessretransmissions of the COBRA schedule frames before rescheduling thesub-channel or frequency resource.

Alternatively, if there is no additional STA waiting for transmission,the AP may choose to work on a narrow band, or allocate STA-1 (i.e., theSTA with ACK feedback) to the entire bandwidth. For example, if thereare only two STAs, STA-1 and STA-2, waiting for transmission and the APfails to set up connection with one of the STAs (i.e., STA-2), the APmay choose to only operate on the primary 20 MHz sub-channel and keepthe TXOP for STA-1. Alternatively, the AP may allocate the entire 40 MHzchannel to STA-1 if STA-1 is capable of operating on the 40 MHzbandwidth.

FIG. 17 is a diagram of an example transmission failure in one of thesub-channels in DL COBRA 1700. In this example, an AP 1705, a STA-1 1710and a STA-2 1715 are shown. The AP 1705 may be operating on a 40 MHzchannel, which may include two 20 MHz sub-channels. It should be notedthat this is for illustrative purposes only and the AP may be operatingon any channel size or configuration. Once the AP 1705 acquires thechannel, the AP 1705 may assign STA-1 1710 to the first 20 MHzsub-channel and STA-2 1715 to the second 20 MHz sub-channel. The AP mayassign the channels in accordance with the procedures described above.The AP 1705 may transmit a COBRA schedule frames 1720 a, 1720 b to STA-11710 and STA-2 1715 on their respective 20 MHz sub-channels. The COBRAschedule frames 1720 a, 1720 b may include data packet size informationand may indicate when each STA is expected to receive their respectivedata packets. STA-1 1710 and STA-2 1715 may confirm by transmitting ACKs1725 a, 1725 b to the AP 1705. The AP 1705 may then transmit DL packets1730 a to STA-1 1710 and 1730 b to STA-2 1715. As shown in FIG. 17, theDL data packet 1730 a intended for STA-1 1710 is larger than the DL datapacket 1730 b intended for STA-2 1715. The AP 1705 may pad zeroes in thetail of DL data packet 1730 b to align the packet size with DL datapacket 1730 a in order to keep control of the TXOP over allsub-channels. In this example, COBRA schedule frames 1720 a, 1720 bindicated that both STA-1 1710 and STA-2 1715 are expected to receivetheir respective data packets at time to. If one or more STAs have notreceived the packet by the time indicated in the COBRA schedule frame,the STAs may transmit back a NACK frame to the AP. This may occur a SIFSafter to. In this example shown in FIG. 17, STA-1 1710 receives DL datapacket 1730 a by to. Therefore, STA-1 1710 sends ACK 1735 to AP 1705 toconfirm. STA-2 1715, however does not receive DL data packet 1730 b byto and sends NACK 1740 to AP 1705.

In the event of such a transmission failure, the AP may employ variousoptions. For example, the AP may choose to transmit the DL data packetsto the same group of STAs as in the previous transmission. Prior totransmitting the DL data packets, the AP may choose to modify thechannel assignment for the group of STAs. The transmission to the groupof STAs which failed to receive the previous DL data packets may beretransmissions of the previous data packet or may be new transmissions.However, it should be noted that retransmissions may be scheduled laterto achieve better time diversity.

Alternatively, the AP may transmit to a different group of STAs otherthan the previous transmission. The different group of STAs may haveoverlap with the previous group of STAs. For example, the AP maytransmit to STA-1, a member of a previous group of STAs whichsuccessfully received the DL data packet, and STA-3, a STA that was notin the original group of STAs. Alternatively, if STA-1 successfullyreceived the DL data packet in a first transmission, the AP may transmitto STA-2, the member in the previous group of STA which failed, andSTA-3, a new STA. In this case, the transmission to STA-2 may be aretransmission or a new transmission. The sub-channel assignment for thenew group of STAs may be independent of the previous transmission.Alternatively, the AP may transmit to one STA using the entirebandwidth, of may choose to transmit to a certain number of STAs of thegroup of STAs using only a part of the bandwidth, e.g., the AP maytransmit to STA-1 using a 20 MHz sub-channel only. It should be notedthat these transmission failure methods and procedures described hereinmay be used in any of the examples described herein with respect to bothuplink and downlink transmission failures.

FIG. 18 is a diagram of an example transmission failure of COBRA pollinformation in UL COBRA 1800. In this example, an AP 1805, a STA-1 1810,a STA-2 1815 and a STA-3 1820 are shown. The AP 1805 may be operating ona 40 MHz channel, which may include two 20 MHz sub-channels. Once the AP1805 acquires the channel, it may attempt to assign the two sub-channelsto STA-1 1810 and STA-2 1815, respectively. To assign the twosub-channels, the AP 1805 may perform a polling procedure. The AP 1805may transmit COBRA polling frame 1825 a to STA-1 1810 and COBRA pollingframe 1825 b to STA-2 1815 on their assigned 20 MHz sub-channels. STA-11810 and STA-2 1815 may each transmit ACK frames 1830 a, 1830 b to theAP 1805. In this example, the AP 1805 fails to receive ACK 1830 b fromSTA-2 1815. In this case, the AP 1805 may transmit COBRA polling frames1835 a, 1835 b to STA-1 1810 and STA-2 1815. Again, in response, STA-11810 and STA-2 1815 may each transmit ACK frames 1840 a, 1840 b to theAP 1805.

If the AP still doesn't receive an ACK from one or more STAs, and aretransmission time achieves a maximum predetermined value the AP maychoose to poll another STA. In this example, the AP 1805 again fails toreceive ACK 1840 b from STA-2 1815. As a result, the AP 1805 performsanother polling procedure and transmits COBRA polling frame 1845 a toSTA-1 1810 and COBRA polling frame 1845 b to STA-3 1820. STA-1 1810 andSTA-3 1820 may each transmit ACK frames 1850 a, 1850 b to the AP 1805.If both ACK frames 1850 a, 1850 b are successfully received, the AP 1805may then transmit COBRA schedule frames 1855 a, 1855 b to STA-1 1810 andSTA-3 1820. STA-1 1810 and STA-3 1820 may transmit UL packets 1860 a,1860 b to AP 1805 as scheduled.

It should be noted that the AP may perform more or less retransmissionsof the COBRA polling frames before rescheduling the sub-channel orfrequency resource. Alternatively, if there is no additional STA waitingfor transmission, the AP may choose to work on narrow band, or allocatethe entire bandwidth to the STA with ACK feedback.

FIG. 19 is a diagram of an example transmission failure of COBRAschedule information in UL COBRA 1900. In this example, an AP 1905, aSTA-1 1910 and a STA-2 1915 are shown. The AP 1905 may be operating on a40 MHz channel, which may include two 20 MHz sub-channels. It should benoted that this is for illustrative purposes only and the AP may beoperating on any channel size or configuration. Once the AP 1905acquires the channel, it may attempt to assign the two sub-channels toSTA-1 1910 and STA-2 1915, respectively. To assign the two sub-channels,the AP 1905 may perform a polling procedure. The AP 1905 may transmitCOBRA polling frame 1920 a to STA-1 1910 and COBRA polling frame 1920 bto STA-2 1915 on their assigned 20 MHz sub-channels. STA-1 1910 andSTA-2 1915 may each transmit ACK frames 1925 a, 1925 b to the AP 1905.If both ACK frames are received successfully, the AP 1905 may thentransmit COBRA schedule frames 1930 a, 1930 b to STA-1 1910 and STA-21915. If one of the STAs does not receive the COBRA schedule frame, theSTA and AP may follow one of the following procedures.

In this example, STA-2 1915 fails to receive COBRA schedule frame 1930b, whereas STA-1 1910 correctly receives COBRA schedule frame 1930 a andwill therefore transmit UL packet 1935 a to AP 1905. If the COBRAschedule frames 1930 a, 1930 b are within a fixed length, as shown inthe example provided in FIG. 19, STA-2 1915 may know the expected timeto start transmitting its UL data packet 1935 b. Therefore, the STA-21915 may continue transmitting the UL data packet 1935 b as expected.However, because STA-2 1915 did not receive COBRA schedule frame 1930 b,STA-2 1915 is unaware of the information regarding the maximum packetsize carried in COBRA schedule frame 1930 b. Therefore, STA-2 1915 maynot be able to pad zeroes to the end of UL packet 1935 b to align itspacket size with that with UL packet 1935 a transmitted by STA-1 1910.In this case, AP 1905 may be at risk of losing the media of thesub-channel allocated to STA-2 1905.

Alternatively, the STA which fails to receive the COBRA schedule framemay choose to do nothing. In this case, an unintended STA may transmitover the corresponding sub-channel(s), and as a result, the AP may losecontrol of the sub-channel(s). To combat this situation, the AP maymonitor the sub-channels when it receives UL packets from other STAsscheduled for transmission. If the sub-channels are free for a certainperiod, for example, DIFS time before the next packet expected to betransmitted from the AP if the COBRA TXOP is not lost, the AP may resumethe COBRA TXOP. Otherwise, the AP may choose to terminate the currentCOBRA TXOP or continue the COBRA TXOP on the unaffected sub-channels.

FIG. 20 is a diagram of an example transmission failure in one of thesub channels in UL COBRA 2000. In this example, an AP 2005, a STA-1 2010and a STA-2 2015 are shown. The AP 2005 may be operating on a 40 MHzchannel, which may include two 20 MHz sub-channels. Once the AP 2005acquires the channel, it may attempt to assign the two sub-channels toSTA-1 2010 and STA-2 2015, respectively. To assign the two sub-channels,the AP 2005 may perform a polling procedure. The AP 2005 may transmitCOBRA polling frame 2020 a to STA-1 2010 and COBRA polling frame 2020 bto STA-2 2015 on their assigned 20 MHz sub-channels. STA-1 2010 andSTA-2 2015 may each transmit ACK frames 2025 a, 2025 b to the AP 2005.If both ACK frames are received successfully, the AP 2005 may thentransmit COBRA schedule frames 2030 a, 2030 b to STA-1 2010 and STA-22020. STA-1 2010 and STA-2 2015 may transmit UL data packets 2035 a,2035 b to AP 2005 as scheduled. If the AP has not received the packetfrom one or more STAs at expected time, it may transmit back a NACKframe or a NACK frame with COBRA schedule information to the one or moreSTAs a SIFS after time to. In this example, AP 2005 receives UL datapacket 2035 a from STA-1 2010, but does not receive UL data packet 2035b from STA-2. As a result, the AP 2005 may transmit an ACK with the nextCOBRA schedule frame 2040 to STA-1 2010 and a NACK with the next COBRAschedule frame 2045 to STA-2 2015. The AP may employ any of the methodsdescribed herein that may occur after the transmission failure.

FIG. 21 is a diagram of an example NACK control frame 2100 that may beused in the methods described heretofore. The NACK control frame 2100may be identified by a combination of its type, subtype, or extensionfield. Referring to FIG. 21, the NACK control frame 2100 may include aframe control field 2105, a duration field 2110, a receiver address (RA)field 2115, and a frame check sequence (FCS) field 2120.

In the frame control field 2105, the type and the subtype fields mayindicate that the frame is a NACK frame. In another design, the framecontrol field 2105, or another field in the frame, or the PLCP/MACheader may contain an extension field indicating the frame is NACKframe. Such an extension field may be interpreted independently, or incombination with the type and/or subtype field. The type of NACK framemay be set as management, control, data or extension.

In the duration field 2110, single protection settings for both TXOP andnon-TXOP holders may be included. For example, if a failed receivingframe is the final frame in a TXOP or the subsequent transmission orretransmission of that frame plus any expected acknowledgement for thatframe is larger than the remaining TXNAV timer value, the duration field2110 may be set to 0. Otherwise, the duration field 2010 may be set asthe time required to transmit or retransmit that frame, including anyexpected acknowledgement for that frame.

Alternatively, in the duration field 2110, multiple protection settingsfor TXOP holder, e.g., the AP, and for non-TXOP holders, e.g., STAs, maybe included.

For example, for a TXOP holder, if a failed receiving frame is the finalframe in a TXOP or the subsequent transmission or retransmission of thatframe plus any expected acknowledgement for that frame is larger thanthe remaining TXNAV timer value, it may be set to 0. Otherwise, it maybe set as the remaining duration of the TXOP.

For a non-TXOP holder, if the failed receiving frame is the final framein a TXOP or the subsequent transmission or retransmission of that frameplus any expected acknowledgement for that frame is larger than theremaining TXNAV timer value, it may be set to 0, otherwise, it may beset as the remaining duration of the TXOP, or a time for a multipleframe transmission.

The RA field 2115 may indicate the receiving STA or AP's address, whichmay be implemented as a MAC address, an association ID (AID), a partialassociation ID (PAID), or the like.

The frame check sequence (FCS) field 2120 may be included in the designof the NACK.

Uplink COBRA Channel Access

In order to perform uplink COBRA scheduling for STAs, the AP may need toknow which STAs have uplink traffic to transmit. Reliable and efficientuplink data buffer status feedback or polling schemes for uplink COBRAmay be used. Information of the STA data buffer status may becommunicated to the AP efficiently for uplink COBRA transmissionscheduling, especially in scenarios with a large number of STAs. Adedicated random access sub-channel may be utilized. Alternatively, arestricted access window (RAW) for uplink random access may be used.

In uplink COBRA, the AP may select and schedule the STAs that arepermitted to transmit in a COBRA resource. As such, when a STA has datato transmit, there may be a need for the STA to be able to communicatethis information efficiently. This may be implemented by a COBRA randomaccess channel in which each user transmits the information needed tothe AP in one or more dedicated time-frequency resources or sub-channel.The information from different STAs may be separated by an orthogonal orsemi-orthogonal sequence with an associated sequence ID.

In a scenario where there are a large number of STAs (such as in IEEE802.11 High Efficiency WLAN (HEW)), the length of the sequence needed toensure orthogonality may be large and as such may utilize resources thatmay be better for data transmission. In this case, a RAW aided randomaccess channel (RAC) may be used. In this example, the STAs may begrouped and a specific RAC may be restricted to desired group(s). Assuch the sequence length may be reduced and sequence IDs may be reusedin the different groups.

FIG. 22 is a diagram of an example uplink data buffer status feedbackprocedure 2200. Referring to FIG. 22, at step 2205, the AP and STA(s)may exchange capability information to indicate their support for RAWaided RACs. The AP may indicate the parameters of the restricted accesswindow. The parameters specified may include periodic or slot based, RAWID and RAW duration. For example, with periodic RAW aided RAC, the RAWmay be assigned periodically in the following beacon intervals. In thisexample, the RAC RAW may be present every N beacon interval. With slotbased RAC RAW, the RAW may be slotted, and each non-AP STA may begintransmission only at the beginning of each slot. The non-AP STA may alsoneed to restrict the transmission duration within a slot. The non-AP STAmay randomly select a slot to transmit. This may reduce the collisionprobability. At step 2210, each STA that associates with the AP may beassigned a one or more RAW IDs and corresponding sequence IDs. In oneembodiment, the STA may be assigned a RAWID+sequence ID to enable accessfor a limited number of STAs and a separate RAWID+sequence ID to allowall STAs in the network to compete for the random access channel.

At step 2215, the AP may transmit out a RAW aided random access channelannouncement at specific sub-channels (time-frequency resources). Thisannouncement may contain the RAW ID of the RAC and the resources used,for example, duration and frequency band. At step 2220, a STA that hasdata to transmit randomly may access the random access channel using thesequence specified by its sequence ID during a permitted time. At step2225, the STA may transmit information indicating parameters such as thedata duration, preferred resources, the data periodicity, and the like.

At step 2230, the AP may correlate the received information using allvalid sequences. A restricted subset of the STAs may be used; thedecoding process becomes more efficient. At step 2235, the AP mayidentify STAs with data to transmit and may place them in its schedulingqueue for future scheduling.

Enhanced COBRA Grouping

Current grouping procedures and group maintenance procedures for COBRAschemes allow an AP to conduct grouping of STAs mostly on the basis ofchannel parameters such as propagation path loss, propagation delay, andhardware characteristics, such as clock drift and offset. Currently, noconsideration may be given to other aspects such as traffic requirementsof STAs as well as STA priorities in grouping decisions. Theserequirements are important and therefore, it is desirable to havedetailed (ad hoc) grouping procedures that also take into account eachSTA's traffic requirements such as traffic priorities, applicationtraffic stream durations, and the like.

If an AP or a STA is capable of COBRA, it may include a COBRAcapability/operation element in its beacons, probe request/response,association request/response, (Re)association request/response, or othertypes of frames such as management, control or extension frames. FIG. 23is a diagram of an example COBRA capability/operation element 2300.Referring to FIG. 23, the example COBRA capability/operation element maycontain element ID field 2305, a length field 2310, a COBRA resourcesfield 2315, a preferred resources field 2320, a modulation and codingset (MCS) field 2325, a priority grouping field 2330, an applicationbased grouping field 2335, and an ad hoc grouping field 2340.

The element ID field 2305 may indicate that the element is a COBRACapability/Operation element.

The length field 2310 may indicate the length of the COBRACapability/Operation element.

The COBRA resources field 2315 may indicate the COBRA resources that thetransmitting STA or AP is capable of using or that the current BSS uses.This field may contain two subfields: COBRA resource type and COBRAresource specification.

The COBRA resource type subfield may indicate the type of COBRAResources that the transmitting STA or AP is currently using or iscapable of using. This subfield may have the following values: channel,sub-channel, subcarrier groups, and resource blocks. A channel mayinclude channels of certain bandwidths, such as a 20 MHz channel, whichare used as the basic blocks of COBRA resources. A sub-channel mayinclude a fraction of the operating channel that is used as the basicblocks of COBRA resources. Subcarrier groups may include one or moresubcarriers, potentially in pre-defined patterns, which are used as thebasic blocks of COBRA resources. Resource blocks (RBs) may include aresource block and is used as the basic blocks of COBRA resources.

The COBRA Resource Specification subfield may specify the particularCOBRA resources that the transmitting STA or AP is currently using or iscapable of using. The COBRA Resource Specification subfield may beimplemented in various ways. For example, a bitmap may be used toindicate the list of channels or sub-channels, subcarrier groups or RBs,that are currently being used or that the transmitting STA or AP iscapable of using. In another example, an integer may be used to indicatea pre-defined pattern of COBRA resources.

The preferred resources field 2320 may be used by a STA to indicate toan AP which COBRA resource it prefers to use. The implementation of thepreferred resources field 2320 may be similar to that of the COBRAResources field 2315 or similar to the COBRA Resources Specificationsubfield as described above.

The MCS field 2325 may be used by a STA to indicate to an AP which MCSit prefers, potentially over the preferred resources indicated.

The priority grouping field 2330 may indicate whether the transmittingSTA or AP is capable of supporting priority grouping.

The application based grouping field 2335 may indicate whether thetransmitting STA or AP is capable of supporting application basedgrouping.

The ad hoc grouping field 2340 may indicate whether the transmittingSTA/AP is capable of supporting ad hoc grouping.

It may be understood that the COBRA capability/operation element or anyset or subset of fields or subfields thereof may be implemented as anypart of new or existing elements, such as a HEWNHSE capability element,a HEWNHSE operation element, a COBRA element, or as any part of amanagement, control, null data packet (NDP) or extension frame,including MAC and PLCP headers.

COBRA capability indication procedures using the COBRAcapability/operation element as described herein, will now be describedmaking reference to FIG. 23. A COBRA capable AP may include a COBRAcapability/operation element 2300 in its (short) beacon to indicatewhether the AP is capable of priority grouping, application basedgrouping and ad hoc grouping. In addition, the AP may indicate the typeof COBRA resources (such as channels, sub-channels, subcarrier groups,or resource blocks) being used in its BSS as well as the details onwhich COBRA resources are used in the BSS in the COBRA resources field2315.

A STA, if capable of COBRA, may include a COBRA capability/operationelement 2300 in its probe request, association request, (Re)associationrequest, or other types of frames such as management frames, controlframes, extension frames, NDP frames, action frames or action frameswith no ACK frames, to indicate its COBRA capabilities to one or moreAPs. For example, the STA may use the COBRA resource field 2315 toindicate the type, as well as the particular selection of the COBRAresources, that the STA is capable of using. The STA may also use thepreferred resource field 2320 to indicate to the AP a selection of COBRAresources (such as one or more channels, sub-channels, subcarrier group,RBs or the like) during or after association with an AP, or another STA.Such a preferred resource indication may be based on the measurement ofpackets received by the transmitting STA from the APs or other STAs.

An AP or a STA may include an indicator, such as one bit, of COBRAcapability in the HEW/VHSE capability/operation element or anywhere inits (short) beacon, probe response, association response,(Re)association response, or other type of frames. The positive settingof the COBRA capable indicator may imply that a COBRAcapability/operation element is included in the same packets.Alternatively, including a COBRA capability/operation element may implythat the AP or STA is COBRA capable.

An AP, when receiving a probe request from a STA may decide not torespond to the probe request due to the COBRA capabilities indicated bythe STA in the probe request.

An AP, when receiving a (Re)association request from a STA may rejectthe (Re)association request based on the COBRA capabilities indicated bythe STA in the (Re)association request. If the AP accepts the(Re)association request, it may assign the requesting STA in a COBRAgroup with assigned COBRA resources and respond to the STA with a(Re)association response frame that includes a COBRA group assignmentelement.

Additional access categories may be defined for future generations ofWLAN systems such as HEW or VHSE in addition to the current four accesscategories (ACs) such as AC_VO (voice), AC_VI (video), AC_BE (besteffort), AC_BK (background). Some of the new ACs may include: AC_Gaming(this category is meant for traffic flows associated with real-time andinteractive gaming); AC_VideoConferencing (this AC is meant for trafficflows for real-time video conferencing); AC_PCDisplay (this AC is meantfor traffic flows for PC wireless displays); AC_(V)HDVideo (this AC ismeant for HD or Very HD Videos; and AC_ULVideo (this AC is meant fortraffic flows for uplink video traffic).

The newly defined ACs may be associated with different priorities formedium access, such as different values of enhanced distributed channelaccess (EDCA) parameters, hybrid coordination function (HCF) controlledchannel access (HCCA) polling frequencies, frequencies and durations ofscheduled medium access, and the like, as well as allocation ofresources such as more or less COBRA resources allocated to higher orlower priority traffic.

The existing ACs and the newly defined ACs may apply both for individualSTAs or groups of STAs, such as COBRA groups, or multi-user (MU) MIMOgroups, that may conduct concurrent medium access. The groups of STAssuch as the COBRA groups may be associated with a particular AC as wellas the medium access parameters of that AC.

COBRA-capable STAs may be divided into COBRA groups according to thecharacteristics of their applications. A STA, for example, at the startof a high priority traffic flow, may request grouping using the COBRAgrouping request frame, which may specify the traffic load, priority,and type. The AP may respond with a COBRA grouping response frame or aCOBRA grouping management frame to provide grouping of the STA, to groupthe STA with STAs of similar traffic load, priority and/or type. The STAmay then access the medium together with its COBRA group using theassigned priority, using either scheduled or contention-based mediumaccess. When an application terminates, the STA may again use a COBRAgrouping request frame to update the AP of the STA's current trafficspecification. Alternatively, the last packet of the terminating trafficmay contain indications of the end of the current traffic (flows). TheAP may then respond with a COBRA grouping response frame or a COBRAgrouping management frame to update the COBRA grouping.

An AP may conduct ad hoc COBRA grouping for downlink transmissions. Ifan AP has packets buffered for a selection of STAs, the AP may groupseveral STAs that are destinations of the buffered packets bytransmitting an ad hoc grouping management frame.

FIG. 24 is a diagram of an example ad hoc grouping management frame2400. The ad hoc grouping management frame 2400 may be implemented as aHEWNHSE action frame or as a HEW/VHSE action no ACK frame or a publicaction frame. The example ad hoc grouping management frame 2400 mayinclude a MAC Header 2405, an action field 2410, a group ID field 2415,a group duration field 2420, an IDs field 2425, a resource assignmentfield 2430, a transmit power field 2435, and a delay field 2440.

The action field 2410 may include a category subfield and an actiondetails field. The category subfield may indicate HEWNHSE, and theaction detail subfield may indicate that it is an ad hoc groupingmanagement frame. Alternatively, the ad hoc grouping management framemay be defined as an extension frame, or any other type of management,control, NDP or extension frames or as an information element which maybe included in the AP's beacon, short beacon, or any other type ofcontrol, management or extension frames.

The group ID field 2415 may include the ID assigned to the new ad hocgroup, such as a COBRA group, or a MU-MIMO group, or any other type ofMU groups. One or more indicators may also be included to indicatewhether the grouping is for UL only, DL only or both UL and DL.

The group duration field 2420 may specify the duration of the validityof the group assignment. For example, the potential values for groupduration may be specified as N Time Units (TU) or any other time units,such as milliseconds (ms) or microseconds (μs). Group duration may alsobe indefinite or valid until changed. Group duration may also be validfor one transmission only.

The IDs field 2425 may indicate the IDs of the STAs/APs belonging to thead hoc group. This field may contain a fixed number of subfields; eachsubfield may contain the ID of one STA. The ID of each STA may beimplemented using MAC addresses, or association IDs (AID), or any otherIDs that the APs and the STAs agree upon beforehand. The order in whichthe IDs of the STAs are listed in IDs field 2425 may determine the orderof STAs in the group. The order of assignment, e.g., that of resourceassignment, transmit power or delay, for the STAs in any subsequentfields may be determined using the order of the STAs in the group.

The resource assignment field 2430 may indicate the resource assigned toeach STA in the group. This field may include a number of subfields,with each subfield specifying the resource assigned to the STAs in thegroup. The order of the resource assignment subfields may follow thesame order of the IDs subfields. Each resource assignment subfield maybe implemented in several ways. For example, they may be implemented asbitmaps indicating the resources assigned to each STA. Alternatively,they may be implemented as integers which refer to the channels,sub-channels or resource patterns, such as subcarrier patterns or RBpatterns that are pre-defined. Alternatively, if resources are uniformfor each of the STAs in a group, this field may specify the size of theresource, such as the number of subcarriers, channel bandwidth,sub-channel bandwidth allocated for each STA in the group. The resourcesallocated for each STA may be implied by the order of the STAs listed inthe IDs subfield. In another example, this field may specify the size ofthe total available resources to the entire group of STAs, such as thenumber of subcarriers, a total channel bandwidth, a total sub-channelbandwidth, and the like. The resources allocated to each STA may bedivided equally and may be derived based on the other included in theIDs subfield.

The transmit power field 2435 may indicate the transmit power assignedto each STA in the group when conducting UL channel access. The transmitpowerfield 2435 may include a number of subfields, with each subfieldspecifying the transmit power assigned to the STAs in the group. Theorder of the transmit power subfields may follow the same order of theIDs subfields.

The delay field 2440 may indicate the delay assigned to each STA in thegroup when conducting UL channel access. This field may include a numberof subfields, with each subfield specifying the delay assigned to theSTAs in the group. The order of the delay subfields may follow the sameorder of the IDs subfields.

In another design, each ad hoc group management frame or element mayinclude the assignment for multiple groups; each containing the fieldsof group ID, group duration, IDs, resource assignment, transmit powerand delay.

In yet another design, an AP may include multiple ad hoc groupmanagement elements in its beacon, short beacon, or other types ofmanagement, control or extensions frames, with each ad hoc groupingmanagement element for one group of STAs.

FIG. 25 is a diagram of an example ad hoc grouping management andtransmission procedure 2500. Referring to FIG. 25, at step 2505, an APmay evaluate the traffic specifications or traffic load, or trafficdemand of the STAs in its BSS. The AP may also evaluate the packetsbuffered for downlink transmission.

At step 2510, the AP may determine ad hoc groupings of a subset of STAsin its BSS based on the evaluations at step 2505.

At step 2515, the AP may announce the ad hoc grouping by including oneor more ad hoc grouping management element(s) in its beacon, shortbeacon, or any other type of control, management or extension frames.The AP may also announce the ad hoc grouping by transmitting a broadcastad hoc grouping management frame. If the AP needs to update the variousassignments for the STAs of a particular ad hoc group, it may transmit amulti-cast ad hoc grouping management frame with the RA address set tothe group ID or the group address of the targeted ad hoc group.

Once the ad hoc grouping has been announced, at step 2520, the AP maystart transmitting COBRA transmissions to the ad hoc groups on theassigned COBRA resources. The COBRA transmissions may be precededimmediately with the ad hoc group management frames or a beacon, a shortbeacon, or frames that include the ad hoc grouping managementelement(s). The COBRA transmissions may also be preceded by mediumreservation frames such as RTS/CTS exchanges addressed to the COBRA adhoc group. The STAs in the Ad Hoc Group may use the same ad hoc groupfor UL COBRA transmissions.

Enhanced COBRA Channel Access Schemes

In order to achieve the theoretical gains of COBRA in an implementation,reliable and efficient channel access and scheduling schemes may benecessary. In order to fully take advantage of the COBRA scheme, anappropriate design of UL/DL COBRA channel access schemes may be needed.Several channel access schemes have been designed and discussed. Morechannel access schemes, which are slightly different from the existingschemes, may be designed and developed when implementing the COBRAschemes.

Several frame formats for COBRA DL schedule frames may be used forreliable and efficient channel access and scheduling schemes.

FIG. 26 is a diagram of an example COBRA DL schedule frame 2600. TheCOBRA DL schedule frame 2600 may include a MAC header 2605, a channelassignment field 2630 and an FCS field 2660. The MAC header 2605 mayinclude a frame control field 2610, a duration field 2615, an RA field2620 and a TA field 2625. The channel assignment field 2630 may includea MAP field 2635 and STA channel assignment fields 2640 a-2640 n.

Within the frame control field 2610, a combination of type value andsubtype value fields may be used to indicate that the COBRA DL scheduleframe is a COBRA DL schedule frame. For example, type value field=“01”and one of previously reserved value of subtype value for control frames0000-0110 may be used to indicate the COBRA DL schedule frame.Alternatively, type value field=“11” (meaning this is an extensionframe), and one value between 0000 to 1111 of subtype value field may beused to indicate the COBRA DL schedule frame.

The RA field 2620 in MAC header 2605 may include a multicast MAC addressrepresenting a group of STAs if the COBRA group has been formed andidentified by a group address. Alternatively, a broadcast address may beused. If a single user is involved, a unicast address may be used.

The MAP field 2635 may use 1 byte to indicate the length of the channelassignment, the number of channel assignments, and additional optionalinformation fields.

The STA channel assignment fields 2640 a-2640 n may be 2 bytes. Each ofthe STA channel assignment fields 2640 a-2640 n may include an AIDfield, a sub-channel bitmap field, and a reserve field. The AID fieldmay be 12 bits. The sub-channel bitmap may be 2 bits (2 bits for 40 MHzchannel; 4 bits for 80 MHz channel; 8 bits for 160 MHz). The Reservedfield may be 2 bits.

FIG. 27 is a diagram of another example COBRA DL schedule frame 2700.The COBRA DL schedule frame 2700 may include a MAC header 2705, achannel assignment field 2730 and an FCS field 2760. The MAC header 2705may include a frame control field 2710, a duration field 2715, an RAfield 2720 and a TA field 2725. The channel assignment field 2730 mayinclude a STA assignment bitmap field 2735 and channel assignment bitmapfields 2740 a-2740 n.

The frame control field 2710, and the RA field 2720 may be the same asdescribed herein.

The STA assignment bitmap field 2735 may be 1 to Q bytes, depending onthe size of the group addressed by RA field 2720. The bitmap indicatingthe STA may assign at least one channel/band in the COBRA DLtransmission. The length of the bitmap may be the same as the size ofthe configured group identified in RA field 2720. For example, a bitmapof 8 bits (1 Byte) may be used to indicate which STAs within a group of8 STAs are assigned to at least one channel. If a bitmap position is setto “1”, it may mean the corresponding STA may get a DL COBRA assignment.Otherwise, it may not be assigned.

In the channel assignment bitmap fields 2740 a-2740 n, for each positivebitmap position in the preceding STA assignment bitmap, one channelassignment bitmap field/IE may be used to indicate the channelassignment for the assigned STA. The length of the channel assignmentbitmap may be the same as the number of minimum COBRA band (for example,20 MHz) in the system. For example, a channel assignment bitmap of 4bits maybe used to represent channel assignment of 20 MHz channels/bandsin a system with 80 MHz channel.

FIG. 28 is a diagram of an example COBRA UL schedule frame 2800. TheCOBRA UL schedule frame 2800 may include a MAC header 2805, a controlinformation field 2830 and an FCS field 2880. The MAC header 2805 mayinclude a frame control field 2810, a duration field 2815, an RA field2820 and a TA field 2825. The control information field 2830 may includea power control field 2835, a time offset field 2840, a frequency offsetfield 2845 and an UL SIG field 2850.

The COBRA UL schedule frame 2800 may be a unicast frame. For example,COBRA UL Schedule frames transmitted over different sub-channels may bedifferent.

Within the frame control field 2810, a combination of type value andsubtype value fields may be used to indicate that this frame is a COBRAUL schedule frame. For example, type value field=“01” and one of apreviously reserved value of subtype value for control frames 0000-0110may be used to indicate the COBRA UL schedule frame. Alternatively, typevalue field=“11” (meaning this is an extension frame), and one valuebetween 0000 to 1111 of subtype value field may be used to indicate theCOBRA UL schedule frame.

The RA field 2820 in MAC header 2805 may include a multicast MAC addressrepresenting a group of STAs, if the COBRA group has been formed andidentified by the group address. Alternatively, the RA field 2820 mayinclude a Broadcast address. If a single user is involved, the RA field2820 may include a Unicast address.

The control information field 2830 may be optional. If the RA field 2820in the MAC header 2805 is a unicast address, the power control field2835 may be the power control command, relative power control command oran absolute level of transmit power for the addressed STA to apply inits uplink COBRA transmission. If the RA field 2820 in the MAC header2805 is a group address, e.g., an address for a group of N STAs, thepower control may be a field of N×M bits, where the M bits is the powercontrol command, the relative power control command, or the absolutelevel of transmit power of each STA in the group to apply in its uplinkCOBRA transmission.

If the RA field 2820 in the MAC header 2805 is a unicast address, thetime offset field 2840 may be the time offset or the relative timeoffset that the addressed STA may apply in its uplink COBRAtransmission. If the RA field 2820 in the MAC header 2805 is a groupaddress, e.g., for a group of N STAs, the time offset field 2840 may bea field of N×P bits, where the P bits is the timing offset that each STAin the group may apply in its uplink COBRA transmission.

If the RA field 2820 in the MAC header 2805 is a unicast address, thefrequency offset field 2845 may be the time offset or the relative timeoffset that the addressed STA may apply in its uplink COBRAtransmission. If the RA field 2820 in the MAC header 2805 is a groupaddress, e.g., for a group of N STAs, the frequency offset filed 2840may be a field of N×P bits, where the P bits is the frequency offsetthat each STA in the group may apply in its uplink COBRA transmission.

The UL SIG field 2850 may be the SIG field that the addressed STA mayapply in its SIG field in the PLCP header in the uplink COBRAtransmission.

Alternatively, a unified design of a COBRA UL/DL schedule frame may beused.

FIG. 29 is a diagram of a first example of a unified COBRA UL/DLschedule frame 2900. The unified COBRA UL/DL schedule frame 2900 mayinclude a MAC header 2905, a channel assignment field 2930, a controlinformation field 2945 and an FCS field 2950. The MAC header 2905 mayinclude a frame control field 2910, a duration field 2915, an RA field2920 and a TA field 2925. The channel assignment field 2930 may includea STA assignment bitmap and UL/DL direction field 2935 and channelassignment bitmap fields 2940 a-2940 n.

The same fields as in the COBRA DL schedule frames described herein maybe included. The type value and subtype value combination in the framecontrol field 2910 in MAC header 2905 may indicate this frame is theunified COBRA UL/DL schedule frame. The control information field 2945may be optional. The same fields as in the COBRA UL schedule framesdescribed herein may be included. For example, the control informationfield 2945 may include a power control field, a time offset field, afrequency offset field, and a UL SIG field. A DL SIG field may also beincluded and it should be noted that the control information field 2945may include information for both the uplink and downlink. In thisexample, an UL/DL direction indicator may be included in the STAassignment bitmap field 2935. One of the reserved bits in the channelassignment bit map may be included.

FIG. 30 is a diagram of a second example of a unified COBRA UL/DLschedule frame 3000. The unified COBRA UL/DL schedule frame 3000 mayinclude a MAC header 3005, an UL/DL direction field 3030, a channelassignment field 3035, an UL control information field 3050 and an FCSfield 3055. The MAC header 3005 may include a frame control field 3010,a duration field 3015, an RA field 3020 and a TA field 3025. The channelassignment field 3035 may include a STA assignment bitmap field 3040 andchannel assignment bitmap fields 3045 a-3045 n.

The same fields as in the COBRA DL schedule frames described herein maybe included. The type value and subtype value combination in the framecontrol field 3010 in MAC header 3005 may indicate this frame is theunified COBRA UL/DL schedule frame. The uplink control information field3045 may be optional. The same fields as in the COBRA UL schedule framesdescribed herein may be included. For example, the UL controlinformation field 3050 may include a power control field, a time offsetfield, a frequency offset field, and a UL SIG field.

In this example, a standalone UL/DL direction indicator field 3030 isused. Alternatively, an UL/DL direction indicator may be used in thePLCP header.

FIG. 31 is a diagram of a first example COBRA poll frame 3100. The COBRApoll frame 3100 may include a MAC header 3105, a COBRA poll informationfield 3130 and an FCS field 3145. The MAC header 3105 may include aframe control field 3110, a duration field 3115, an RA field 3120 and aTA field 3125. The COBRA poll information field 3130 may include a MAPfield 3135 and STA information fields 3140 a-3140 n.

Within the frame control field 3110, a combination of type value andsubtype value fields may be used to indicate this frame is COBRA pollschedule frame. For example, type value field=“01” and one of previouslyreserved values of subtype value for control frames 0000-0110 may beused to indicate the COBRA poll schedule frame. Alternatively, typevalue field=“11” (meaning this is an extension frame), and one valuebetween 0000 to 1111 of subtype value field may be used to indicate theCOBRA poll schedule frame.

For the RA field 3120 in the MAC header 3105, a multicast MAC addressrepresenting a group of STAs, if the COBRA group has been formed andidentified by the group address may be used. Alternatively, a Broadcastaddress may be used. If a single user is involved, a unicast address maybe used.

The MAP field 3135 may be 1 Byte and may indicate the length of the STAinformation fields 3140 a-3140 n, the number of STA information field3140 a-3140 n, and additional optional information fields. The STAinformation fields 3140 a-3140 n may include an AID field to identifythe STA, channel assignment fields, sub-channel bitmap fields toindicate the potential sub-channel(s) assigned to each STA, and a numberof reserved fields.

The channel assignment fields may each be 2 Bytes. The AID fields mayeach be 12 bits. The sub-channel bitmap fields may each be 2 bits (2bits for 40 MHz channel; 4 bits for 80 MHz channel; 8 bits for 160 MHz).The reserved field may be 2 bits.

FIG. 32 is a diagram of a second example COBRA poll frame 3200. TheCOBRA poll frame 3200 may include a MAC header 3205, a poll informationfield 3230 and an FCS field 3245. The MAC header 3205 may include aframe control field 3210, a duration field 3215, an RA field 3220 and aTA field 3225. The poll information field 3230 may include a STA pollbitmap field 3235 and control info of ULR j-n fields 3240 a-3240 n.

The frame control field 3210 and RA field 3220 in the MAC header 3205may be the same as in the examples described herein.

The STA poll bitmap field 3235 may include 1 to Q bytes, depending onthe size of the group addressed by RA field 3220. The STA poll bitmapfield 3235 may indicate the STA being polled by the AP. The length ofthe STA poll bitmap field 3235 may be the same as the size of theconfigured group identified in RA field 3220. For example, a bitmap of 8bits (1 Byte) may be used to indicate which STAs within a group of 8STAs are assigned at least one channel. If a bitmap position is set to“1”, it may mean the corresponding STA is polled. Otherwise, that STAmay not be polled.

The control info of ULR j-n fields 3240 a-3240 n each contain controlinformation of the upcoming j^(th) ULR and 1≤j≤J. The AP polls J STAsfor ULR, thus the AP may needs to schedule the transmission of J ULRs ina way that reduces potential collisions. The control info if ULR j-nfields 3240 a-3240 n may each may include a channel bitmap k (1≤k≤N) andcode domain (CDM), time domain (TDM) or frequency domain (FDM)information. For each positive bitmap position in the preceding STAassignment bitmap, one channel assignment bitmap field/IE may be used toindicate the channel assignment for the assigned STA. The length of thechannel assignment bitmap may be the same as the number of minimum COBRAbands (for example, 20 MHz) in the system. For example, a channelassignment bitmap of 4 bits may be used to represent channel assignmentof 20 MHz channels/bands in a system with 80 MHz channel. The upcomingmultiple ULR transmissions may be separated by CDM, TDM or FDM. WithCDM, the AP and STAs may agree with a pre-defined set of orthogonalsequences and each STA may be assigned one sequence. The polled STAs mayapply assigned dedicated sequences to the ULR transmission. With TDM,the polled STAs may transmit ULR frames sequentially one after another.With FDM, the polled STAs may transmit ULR frames on pre-assignedfrequency sub-channels.

FIG. 33 is a diagram of an example COBRA uplink request (ULR) frame3300. The COBRA ULR frame 3300 may include a MAC header 3305, an ULdetails field 3330 and an FCS field 3345. The MAC header 3305 mayinclude a frame control field 3310, a duration field 3315, an RA field3320 and a TA field 3325. The UL details field 3330 may include a sizeof data or buffer occupancy field 3335 and an optional delay requirementfield 3340.

Within the frame control field 3310, a combination of type value andsubtype value fields may be used to indicate that this frame is a COBRAULR frame. For example, type value field=“01” and one of previouslyreserved value of subtype value for control frames 0000-0110 may be usedto indicate the COBRA ULR frame. Alternatively, type value field=“11”(meaning this is an extension frame), and one value between 0000 to 1111of subtype value field may be used to indicate the COBRA ULR frame.

The size of data (or buffer occupancy) field 3335 in the UL detailsfield 3330 may include the amount of data at the STA. The delayrequirement field 3340, which may be an optional field, may include themaximum allowed delay associated with the data.

The COBRA ACK/NACK frames described herein may be combined orpiggybacked with other frames, such as ULR or data frames. For example,COBRA schemes may allow ACK/NACK frames aggregated with other frames inthe using an example A-MPDU format as shown in FIG. 34.

FIG. 34 is a diagram of an example A-MPDU format used to piggyback anACK frame to another frame. In this example, a first A-MPDU subframe3405 and a second A-MPDU subframe 3450 are shown. A-MPDU subframe 3405may include the MPDU delimiter 3410, MPDU 3415, pad 3420, as well asother optional fields. The MPDU delimiter 3410 may include a reservedfield 3425, MPDU length field 3430, CRC field 3435, and a delimitersignature field 3440, as well as some reserved bits.

The second A-MPDU subframe 3450 includes an ACK. However, the secondA-MPDU subframe 3450 may instead include a NACK. As shown the secondA-MPDU subframe 3450 containing the ACK is aggregated with otherA-MPDUs, e.g. A-MPDU subframe 3405. The entire A-MPDU frame may bepassed to PHY layer to transmit.

Using the A-MSDU format. The aggregated frames defined for contentionfree (CF) transmissions may be reused, and the A-MSDU structure may becontained in the frame body of a single MPDU. For example, the COBRAscheme may reuse the QoS+CF-ACK frame by defining subtype as 1001. Inorder to piggyback a NACK frame with the other frame, a new subtype maybe defined.

Several methods for standalone uplink COBRA channel access will now bedescribed. In a first embodiment, a fixed or specific band assignmentfor ULR frame transmission for each STA may be used. In a secondembodiment, a code division multiplex (CDM) ULR frame may be transmittedon all bands with sounding and frequency-selective COBRA transmissionscheduling information. In a third embodiment, a time division multiplex(TDM) ULR frame may be transmitted on all bands with sounding andfrequency-selective COBRA transmission scheduling information.

FIG. 35 is a diagram of a first example channel access scheme forstandalone UL COBRA using a fixed or specific band assignment for ULRframe transmission for each STA. In this example, an AP 3505, a STA-13510 and a STA-2 3515 are shown. The AP 3505 may be operating on a 40MHz channel, which may include two 20 MHz sub-channels. It should benoted that this is for illustrative purposes only and the AP may beoperating on any channel size or configuration. The AP 3505 performs apolling procedure and transmits COBRA polling frame 3520 a to STA-1 3510and COBRA polling frame 3520 b to STA-2 3515 on their separaterespective channels. Alternatively, the poll may be sent to all targetSTAs (configured in a group) on all channels.

There may be several options to signal the information in the COBRApolling frames. For example, the AP may configure the mapping betweenspecific STAs and corresponding channels where the COBRA polls aretransmitted beforehand. For example, as shown in FIG. 35, STA-1 3510 ispreconfigured to transmit its ULR frame 3525 a on its respectiveseparate 20 MHz channel and STA-2 3515 is preconfigured to transmit itsULR frame 3525 b on its respective separate 20 MHz channel.Alternatively, the COBRA polling frames may contain specific bandassignments for ULR frame transmission for each STA.

If the AP configured the mapping between specific STAs and correspondingchannels beforehand using, for example, previous control or managementframes, the STAs in the previously configured group may wake up at thebeginning of the COBRA polling frames transmitted by the AP and listenfor the polling on all channels or preconfigured channels/bands.

After receiving valid COBRA polling frames 3520 a, 3520 b from the AP3505, if the STAs 3510, 3515 have uplink data to transmit, the STAs3510, 3515 may transmit a ULR frame 3525 a, 3525 b on the channel thatis either assigned in the COBRA polling frame 3520 a, 3520 b orpreconfigured by previous control or management frames.

Upon receiving ULR frames 3525 a, 3525 b from STA-1 3510 and STA-2 3515,the AP 3505 may determine channel assignment for UL COBRA transmissionand transmit COBRA UL scheduling frames 3530 a, 3530 b on each assignedchannel.

STAs that have transmitted ULR frames may listen on all channels or onlychannels configured previously. After receiving the COBRA UL schedulingframes 3530 a, 3530 b, which contain UL COBRA transmission information,STA-1 3510 and STA-2 3515 may transmit their data frames 3535 a, 3535 bon their assigned channels/bands accordingly. The AP may confirm receiptby transmitting ACKs 3540 a, 3540 b.

FIG. 36 is a diagram of a second example channel access scheme forstandalone UL COBRA with code division multiplex (CDM) ULR. In thisexample, an AP 3605, a STA-1 3610 and a STA-2 3615 are shown. The AP3605 may be operating on a 40 MHz channel, which may include two 20 MHzsub-channels. It should be noted that this is for illustrative purposesonly and the AP may be operating on any channel size or configuration.

AP 3605 may transmit COBRA polling frames 3620 a, 3620 b for all targetSTAs (configured in a group) on all channels, here STA-1 3610 and STA-23615. If the AP configured the mapping between specific STAs andcorresponding channels beforehand using, for example, using previouscontrol or management frames, the STAs in the previously configuredgroup may wake up at the beginning of the COBRA polling framestransmitted by the AP and listen for the polling on all channels orpreconfigured channels/bands.

After receiving a valid COBRA polling frames 3620 a, 3620 b from the AP3605, STA-1 3610 and STA-2 3615, each having uplink data to transmit,may each transmit a ULR frame with sounding signals on all thesub-channels or a preconfigured or signaled subset of all availablesub-channels in the system. In this example, STA-1 3610 transmits ULRframes with sounding signals 3625 a, 3625 b on all of the sub-channels.STA-2 3615 transmits ULR frames with sounding signals 3630 a, 3630 b onall of the sub-channels. Since both STA-1 3610 and STA-2 3615 need torespond to the COBRA polling frame 3620, their respective ULR frameswith sounding signals 3625 a, 3625 b, 3630 a, 3630 b may be transmittedin an orthogonal manner (in time, frequency or code domain). In thisexample, the ULR frames with sounding signals 3625 a, 3625 b, 3630 a,3630 b are transmitted in an orthogonal manner in the code domain.

Upon receiving ULR frames with sounding signals 3625 a, 3625 b, 3630 a,3630 b from STA-1 3610 and STA-2 3615 respectively, AP 3605 maydetermine channel assignments for UL COBRA transmissions. AP 3605 maybase these channel assignments on channel quality, for example using achannel quality indicator (CQI) or some other parameter. AP 3605 maytransmit COBRA UL Schedule frames 3635 a, 3635 b on each assignedchannel.

STAs that have transmitted ULR frames may listen on all channels or onlychannels configured previously. In this example, after receiving theCOBRA UL scheduling frames 3635 a, 3635 b, each of which contains the ULCOBRA transmission information, STA-1 3610 and STA-2 3615 may transmittheir respective data frames 3640 a, 3640 b on the assignedchannels/bands accordingly. The AP 3605 may confirm receipt bytransmitting ACKs 3645 a, 3645 b.

FIG. 37 is a diagram of a third example channel access scheme forstandalone UL COBRA with time division multiplex (TDM) ULR. In thisexample, an AP 3705, a STA-1 3710 and a STA-2 3715 are shown. The AP3705 may be operating on a 40 MHz channel, which may include two 20 MHzsub-channels. It should be noted that this is for illustrative purposesonly and the AP may be operating on any channel size or configuration.

AP 3705 may transmit a COBRA polling frame 3720 for all target STAs(configured in a group) on all channels, here STA-1 3710 and STA-2 3715.If the AP configured the mapping between specific STAs and correspondingchannels beforehand using, for example, using previous control ormanagement frames, the STAs in the previously configured group may wakeup at the beginning of the COBRA polling frames transmitted by the APand listen for the polling on all channels or preconfiguredchannels/bands.

After receiving a valid COBRA polling frame 3720 from the AP 3705, STA-13710 and STA-2 3715, each having uplink data to transmit, may eachtransmit a ULR frame with sounding signals on all the channels or apreconfigured or signaled subset of all available channels in thesystem. In this example, STA-1 3710 transmits ULR frames with soundingsignals 3725 a, 3725 b on all of the channels. STA-2 3715 transmits ULRframes with sounding signals 3730 a, 3730 b on all of the channels.Since both STA-1 3710 and STA-2 3715 need to respond to the COBRApolling frame 3720, their respective ULR frames with sounding signals3725 a, 3725 b, 3730 a, 3730 b may be transmitted in an orthogonalmanner (in time, frequency or code domain). In this example, the ULRframes with sounding signals 3725 a, 3725 b, 3730 a, 3730 b aretransmitted in an orthogonal manner in the time domain.

Upon receiving ULR frames with sounding signals 3725 a, 3725 b, 3730 a,3730 b from STA-1 3710 and STA-2 3715, respectively, AP 3705 maydetermine channel assignments for UL COBRA transmissions. AP 3705 maybase these channel assignments on channel quality, for example using aCQI or some other parameter. AP 3705 may transmit COBRA UL Scheduleframes 3735 a, 3735 b on each assigned channel.

STAs that have transmitted ULR frames may listen on all channels or onlychannels configured previously. In this example, after receiving theCOBRA UL scheduling frames 3735 a, 3735 b, each of which contains the ULCOBRA transmission information, STA-1 3710 and STA-2 3715 may transmittheir respective data frames 3740 a, 3740 b on the assignedchannels/bands accordingly. The AP 3705 may confirm receipt bytransmitting ACKs 3745 a, 3745 b.

Several methods for standalone downlink COBRA channel access will now bedescribed. In a first embodiment, a fixed or specific band assignmentfor downlink COBRA transmission of each STA without an ACK from theassigned STAs may be used. In a second embodiment, a fixed or specificchannel/band assignment for downlink COBRA transmission of each STA withan ACK from the assigned STAs may be used.

FIG. 38 is a diagram of a first example channel access scheme forstandalone DL COBRA using a fixed or specific band assignment fordownlink COBRA transmission of each STA without an ACK from the assignedSTAs. In this example, an AP 3805, a STA-1 3810 and a STA-2 3815 areshown. The AP 3805 may be operating on a 40 MHz channel, which mayinclude two 20 MHz sub-channels. It should be noted that this is forillustrative purposes only and the AP may be operating on any channelsize or configuration.

The AP 3805 may transmit a DL COBRA schedule frame 3820 containing theDL transmission schedule of each channel/band on correspondingchannels/bands. As shown in FIG. 38, the AP may transmit the DL COBRAschedule frame 3820 on a preconfigured set of channels, here only thefirst channel of the set of two channels in this example. Alternatively,the AP may transmit a DL COBRA schedule frame which contains DLtransmission schedule of all assigned channels for all target STAs onall assigned channels, or all channels in the system.

As in the examples above, if the STAs are configured in a group byprevious control or management frames, the configured group may wake upat the beginning of the DL COBRA schedule frames transmitted by the APand listen for the DL COBRA schedule frames on all channels orpreconfigured channels/bands.

After receiving the valid DL COBRA schedule frame 3820 from the AP 3805,the STA-1 3810 and STA-2 3815 may tune their respective receivers to theassigned channels/bands to receive their respective downlink dataframes.

The AP 3805 may start DL COBRA transmission a SIFS time aftertransmitting the DL COBRA schedule frame 3820, by transmitting DL dataframes 3825 a, 3825 b to STA-1 3810 and STA-2 3815, respectively.

If the DL data frames 3825 a, 3825 b are received and decodedsuccessfully, STA-1 3810 and STA-2 3815 may transmit ACKs 3830 a, 3830 bto the AP on channel/band where the corresponding DL data frame 3825 a,3825 b is received.

FIG. 39 is a diagram of a second example channel access scheme forstandalone DL COBRA using a fixed or specific channel/band assignmentfor downlink COBRA transmission of each STA with an ACK from theassigned STAs may be used. In this example, an AP 3905, a STA-1 3910 anda STA-2 3915 are shown. The AP 3905 may be operating on a 40 MHzchannel, which may include two 20 MHz sub-channels. It should be notedthat this is for illustrative purposes only and the AP may be operatingon any channel size or configuration.

The AP 3905 may transmit a DL COBRA schedule frame 3920 containing theDL transmission schedule of each channel/band on correspondingchannels/bands. As shown in FIG. 39, the AP may transmit the DL COBRAschedule frame 3920 on a preconfigured set of channels, here only thefirst channel of the set of two channels in this example. Alternatively,the AP may transmit a DL COBRA schedule frame which contains DLtransmission schedule of all assigned channels for all target STAs onall assigned channels, or all channels in the system.

As in the examples above, if the STAs are configured in a group byprevious control or management frames, the configured group may wake upat the beginning of the DL COBRA schedule frames transmitted by the APand listen for the DL COBRA schedule frames on all channels orpreconfigured channels/bands.

After receiving the valid DL COBRA schedule frame 3920 from the AP 3905,STA-1 3910 and STA-2 3915 may transmit ACKs 3925 a, 3925 b to the AP3905 on their assigned channel(s) to acknowledge that each STA is readyto receive DL frames on the assigned channels. ACK frames 3925 a, 3925 bmay contain NAV or duration information so that STAs near it may settheir NAVs properly upon receiving the ACK. After receiving the DL COBRAschedule frame 3920 from the AP, and either before or after transmittingits ACK, STA-1 3910 and STA-2 3915 may tune their respective receiversto assigned channels/bands to receive their respective downlink dataframes.

The AP 3905 may start DL COBRA transmission a SIFS time after receivingthe ACK frames 3925 a, 3925 b by transmitting DL data frames 3930 a,3930 b to STA-1 3910 and STA-2 3915, respectively. If the DL data frames3930 a, 3930 b are received and decoded successfully, STA-1 3910 andSTA-2 3915 may transmit ACKs 3935 a, 3935 b to the AP 3905 onchannel/band where the corresponding DL data frames 3930 a, 3930 b isreceived.

Several methods for combined downlink/uplink COBRA channel access willnow be described. In a first embodiment, a fixed or specificchannel/band assignment for both uplink and downlink COBRA transmissionis used. In a second embodiment, a fixed or specific channel/bandassignment for downlink but frequency-selective channel/band assignmentfor uplink COBRA transmission may be used.

FIG. 40 is a diagram of a first example combined downlink/uplink COBRAchannel access scheme using a fixed or specific channel/band assignmentfor both uplink and downlink COBRA transmission. In this example, an AP4005, a STA-1 4010 and a STA-2 4015 are shown. The AP 4005 may beoperating on a 40 MHz channel, which may include two 20 MHzsub-channels.

The AP 4005 may transmit DL COBRA schedule frames 4020 a, 4020 b, eachof which contains DL transmission schedule of each channel/band oncorresponding channel/band of STA-1 4010 and STA-2 4015. Alternatively,the AP may transmit a DL COBRA Schedule frame containing DL transmissionschedule of all assigned channels for all target STAs on all assignedchannels, or all channels in the system or a preconfigured set ofchannels.

As in the examples above, if the STAs are configured in a group byprevious control or management frames, the configured group may wake upat the beginning of the DL COBRA schedule frames transmitted by the APand listen for the DL COBRA schedule frames on all channels orpreconfigured channels/bands.

After receiving the valid DL COBRA schedule frames 4020 a, 4020 b fromthe AP 4005, the STA-1 4010 and STA-2 4015 may tune their respectivereceivers to the assigned channels/bands to receive their respectivedownlink data frames.

The AP 4005 may start DL COBRA transmission a SIFS time aftertransmitting the DL COBRA schedule frames 4020 a, 4020 b, bytransmitting DL data frames 4025 a, 4025 b to STA-1 4010 and STA-2 4015,respectively.

If a DL data frame is received and decoded successfully, the STA maytransmit an ACK to the AP on the channel/band where the correspondingdownlink data frame is received. If the receiving STA has uplink data totransmit, it may transmit an “ACK_ULR” frame on the channel/band wherethe corresponding downlink data frame is received. Alternatively, thereceiving STA may transmit an ACK frame with the More Data field set to“1” or “has data”. If a received data frame is not decoded successfullybut the STA has uplink data to transmit, it may transmit an “NACK_ULR”frame on the channel/band where the corresponding downlink data frame isreceived.

In this example, STA-1 4010 successfully receives and decodes the DLdate frame 4025 a intended for it and also has uplink data to transmit,therefore STA-1 4010 transmits an ACK_ULR 4030 to AP 4005. However, theDL data frame 4025 b intended for STA-2 4015 is not received or decodedsuccessfully, but STA-2 4015 has uplink data to transmit. As a result,STA-2 4015 sends a NACK_URL frame 4035 to the AP 4005.

Upon receiving ULR frames 4030, 4035 from STA-1 4010 and STA-2 4015, theAP 4005 may determine channel assignments for UL COBRA transmissions andtransmits COBRA UL Schedule frames 4040 a, 4040 b to STA-1 4010 andSTA-2 4015 on their respectively assigned channels.

STAs that have transmitted ULR frames may listen on all channels or onlychannels configured previously. After receiving the COBRA UL scheduleframes 4040 a, 4040 b, each of which contains the UL COBRA transmissioninformation, STA-1 4010 and STA-2 4015 may each transmit its respectivedata frame 4045 a, 4045 b on the assigned channels/bands accordingly.The AP 4005 may confirm receipt by transmitting ACKs 4050 a, 4050 b.

FIG. 41 is a diagram of a second example combined downlink/uplink COBRAchannel access scheme using a fixed or specific channel/band assignmentfor downlink COBRA transmission and a frequency-selective channel/bandassignment for uplink COBRA transmission. In this example, an AP 4105, aSTA-1 4110 and a STA-2 4115 are shown. The AP 4105 may be operating on a40 MHz channel, which may include two 20 MHz sub-channels.

AP 4105 may transmit DL COBRA schedule frames 4120 a, 4120 b, each ofwhich contains DL transmission schedule of each channel/band oncorresponding channel/band of STA-1 4110 and STA-2 4115. Alternatively,the AP may transmit a DL COBRA Schedule frame containing the DLtransmission schedule of all assigned channels for all target STAs onall assigned channels, or all channels in the system or a preconfiguredset of channels.

As in the examples above, if the STAs are configured in a group byprevious control or management frames, the configured group may wake upat the beginning of the DL COBRA schedule frames transmitted by the APand listen for the DL COBRA schedule frames on all channels orpreconfigured channels/bands.

After receiving the valid DL COBRA schedule frames 4120 a, 4120 b fromthe AP 4105, the STA-1 4110 and STA-2 4115 may tune their respectivereceivers to the assigned channels/bands to receive their respectivedownlink data frames.

The AP 4105 may start DL COBRA transmission a SIFS time aftertransmitting the DL COBRA schedule frames 4120 a, 4120 b, bytransmitting DL data frames 4125 a, 4125 b to STA-1 4110 and STA-2 4115,respectively.

If a DL data frame is received and decoded successfully, the STA maytransmit an ACK to the AP on the channel/band where the correspondingdownlink data frame is received. If the STA has uplink data to transmit,it may transmit an “ACK_ULR” frame with sounding signals on thechannel/band where the corresponding downlink data frame is received.Alternatively, it may transmit an ACK frame with the More Data field setto “1” or “has data” and with sounding signals.

If a DL data frame is not received and decoded successfully but the STAhas uplink data to transmit, it may transmit an “NACK_ULR” frame withsounding signals on the channel/band where the corresponding downlinkdata frame is received. The STA may transmit sounding signals (such asNDP frames) on channels other than the channel/band where thecorresponding downlink data frame is received. If there are multipleSTAs that need to transmit ULR with sounding signals or sounding signalsalone, their frames may be transmitted in an orthogonal manner (in time,frequency or code domain).

In this example, STA-1 4110 successfully receives and decodes the DLdata frame 4125 a intended for it and also has uplink data to transmit.STA-1 4110 transmits an ACK_ULR with sounding signals 4130 to AP 4105.However, the DL data frame 4125 b intended for STA-2 4115 is notreceived or decoded successfully, but STA-2 4115 has uplink data totransmit. As a result, STA-2 4115 sends a NACK_URL frame with soundingsignals 4135 to the AP 4105. STA-1 4110 also transmits sounding frames4140 a on the other 20 MHz channel assigned to STA-2 4115. Likewise,STA-2 4115 also transmits sounding frames 4140 b on the other 20 MHzchannel assigned to STA-1 4110.

Upon receiving ULR frames with sounding signals 4130, 4135 from STA-14110 and STA-2 4115, the AP 4105 may determine the channel assignmentfor UL COBRA transmissions. The AP 4105 may consider the channel quality(such as CQI) in making that determination. The AP 4105 may transmitCOBRA UL Schedule frames 4145 a, 4145 b on each assigned channel.

STAs that have transmitted ULR frames may listen on all channels or onlychannels configured previously. After receiving the COBRA UL scheduleframes 4145 a, 4145 b, each of which contains the UL COBRA transmissioninformation, STA-1 4110 and STA-2 4115 may transmit their respectivedata frames 4150 a, 4150 b on the assigned channels/bands accordingly.The AP 4105 may confirm receipt by transmitting ACKs 4155 a, 4155 b.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

Although the solutions described herein consider 802.11 specificprotocols, it is understood that the solutions described herein are notrestricted to this scenario and are applicable to other wireless systemsas well.

Although SIFS are used to indicate various inter frame spacing in theexamples of the designs and procedures, all other inter frame spacingsuch as RIFS or other agreed time interval could be applied in the samesolutions.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A station (STA) comprising: a receiver configured to receive a frametransmitted to a plurality of STAs, wherein the frame indicates a firstfrequency resource allocated for the STA and a second frequency resourceallocated for another STA of the plurality of STAs; a transmitterconfigured to transmit a data frame using the first frequency resource;and the receiver configured to receive an acknowledgement frame thatacknowledges receipt of the data frame.
 2. The STA of claim 1, furthercomprising: the receiver configured to receive a multi-user (MU) requestto send (RTS) frame transmitted to the plurality of STAs; and thetransmitter configured to transmit a clear to send (CTS) frame inresponse to receipt of the MU RTS frame, prior to transmission of thedata frame.
 3. The STA of claim 2, wherein the CTS frame is transmittedsimultaneously with another CTS frame transmitted by the another STA ofthe plurality of STAs.
 4. The STA of claim 3, wherein the CTS frame andthe another CTS frame are transmitted using frequency resourcesspecified by the MU RTS frame.
 5. The STA of claim 2, wherein the MU RTSframe comprises a duration field to protect the CTS frame, the dataframe and the acknowledgement frame.
 6. The STA of claim 1, wherein theacknowledgement frame is transmitted to the STA and to the another STA.7. The STA of claim 1, wherein the data frame is an orthogonal frequencydivision multiple access (OFDMA) transmission.
 8. A method performed bya station (STA), the method comprising: receiving a frame transmitted toa plurality of STAs, wherein the frame indicates a first frequencyresource allocated for the STA and a second frequency resource allocatedfor another STA of the plurality of STAs; transmitting a data frameusing the first frequency resource; and receiving an acknowledgementframe that acknowledges receipt of the data frame.
 9. The method ofclaim 8, further comprising: receiving a multi-user (MU) request to send(RTS) frame transmitted to the plurality of STAs; and transmitting aclear to send (CTS) frame in response to receipt of the MU RTS frame,prior to transmission of the data frame.
 10. The method of claim 9,wherein the CTS frame is transmitted simultaneously with another CTSframe transmitted by the another STA of the plurality of STAs.
 11. Themethod of claim 10, wherein the CTS frame and the another CTS frame aretransmitted using frequency resources specified by the MU RTS frame. 12.The method of claim 9, wherein the MU RTS frame comprises a durationfield to protect the CTS frame, the data frame and the acknowledgementframe.
 13. The method of claim 8, wherein the acknowledgement frame istransmitted to the STA and to the another STA.
 14. The method of claim8, wherein the data frame is an orthogonal frequency division multipleaccess (OFDMA) transmission.
 15. An access point (AP) comprising: atransmitter configured to transmit a frame to a plurality of stations(STAs), wherein the frame indicates a first frequency resource allocatedfor a STA and a second frequency resource allocated for another STA ofthe plurality of STAs; a receiver configured to receive a first dataframe using the first frequency resource; the receiver configured toreceive a second data frame on the second frequency resource; and andthe transmitter configured to transmit an acknowledgement frame thatacknowledges receipt of the first data frame and the second data frame.16. The AP of claim 15, wherein the acknowledgement frame is transmittedto the STA and to the another STA.
 17. The AP of claim 15, wherein thefirst frequency resource and the second frequency resource are resourcesfor orthogonal frequency division multiple access (OFDMA) transmission.18. A method performed by an access point (AP), the method comprising:transmitting a frame to a plurality of stations (STAs), wherein theframe indicates a first frequency resource allocated for a STA and asecond frequency resource allocated for another STA of the plurality ofSTAs; receiving a first data frame using the first frequency resource;receiving a second data frame on the second frequency resource; and andtransmitting an acknowledgement frame that acknowledges receipt of thefirst data frame and the second data frame.
 19. The method of claim 18,wherein the acknowledgement frame is transmitted to the STA and to theanother STA.
 20. The method of claim 18, wherein the first frequencyresource and the second frequency resource are resources for orthogonalfrequency division multiple access (OFDMA) transmission.